Competitive
tendering rests on one principle: suppliers must decide independently whether
to bid, how to price and what terms to offer. UK public bodies spent £395
billion on procurement in 2024/25, according to the House of Commons Library’s
analysis of the Whole of Government Accounts. Even modest erosion of that
independence carries significant cost. When rivals coordinate rather than
compete, the paperwork of a fair contest can survive while its substance
disappears.
In the United
Kingdom, agreements between undertakings that have as their object or effect
the prevention, restriction or distortion of competition may infringe the
Chapter I prohibition in section 2 of the Competition Act 1998, the principal
statutory framework against which suspected anti-competitive coordination
should be assessed. The Competition and Markets Authority estimates that bid
rigging can inflate the prices public bodies pay by 20% or more, a margin that,
on a single major contract, can run into millions of pounds in avoidable costs.
Collusion rarely
announces itself through confession or a single dramatic event. It tends to
surface through repeated pricing patterns, suspicious withdrawals,
near-identical tender documents, rotating winners, or suppliers that quietly
avoid particular customers and territories. Any one indicator can have an
innocent explanation. The skill lies in recognising when separate anomalies
accumulate into a pattern that ordinary commercial behaviour cannot readily
explain.
Procurement teams
occupy a distinctive vantage point because they see what individual suppliers
cannot. They compare competing prices, evaluate submissions, observe bidder
conduct and retain records across successive competitions. That cumulative
visibility can expose relationships that are invisible within any single
tender: a bid that looks unremarkable on its own may become significant when
set against previous awards, bidder combinations, geographic outcomes, and
shifts in commercial behaviour over time.
Detection
increasingly pairs professional judgement with data. Bid dispersion,
participation rates, win sequences, geographic concentration, supplier
combinations, and pricing correlation can all help surface unusual behaviour
across large datasets, and the CMA is now investing in AI and data science
tools to scan bidding data at scale. Technology sharpens scrutiny, but it
cannot replace context; anomalies still require interpretation against
capacity, cost structures, market design and the realities of the sector
concerned.
Prevention matters
as much as detection. Procurement design can strengthen rivalry or facilitate
coordination: restrictive qualification criteria, predictable supplier lists,
repetitive contract structures and unnecessary disclosure of sensitive information
can reduce competitive tension. Broader participation, proportionate
requirements and carefully managed market engagement make collusion harder to
organise. At the same time, independent bidding declarations and non-collusion
clauses reinforce expectations that suppliers must compete genuinely and
independently for public contracts throughout the procurement process.
Since February 2025,
the Procurement Act 2023 has strengthened exclusion and debarment consequences
for cartel activity, while individuals who agree to rig bids may also face
criminal liability under the Enterprise Act 2002, subject to statutory exclusions
and defences. Effective protection ultimately depends on informed people,
reliable records, and disciplined governance: training, legal awareness, market
intelligence, and data analysis together protect competition, public money, and
confidence in the integrity of public tendering.
The Procurement Professional as the
First Line of Detection
Procurement
professionals sit at the centre of the fight against bid rigging because they
routinely compare prices, documents, bidder behaviour and outcomes across
competing suppliers. A single tender may reveal nothing conclusive, yet
repeated competitions can expose patterns invisible to individual evaluators or
contract managers. The CMA therefore encourages public procurers to remain
alert to suspicious bidding behaviour, recognising that procurement data can
provide an early warning of collusion long before a formal investigation
begins.
That visibility
matters because cartel behaviour is designed to look like independent
competition. Teams may notice identical prices, unusual wording, recurring
withdrawals, uncompetitive bids, or sudden price reductions when an unfamiliar
supplier enters the market. None proves wrongdoing on its own; significance
grows when the same suppliers repeatedly appear together, alternate victories,
avoid particular territories, or behave differently depending on who else is
competing.
The CMA’s guidance
identifies suspicious patterns including identical prices, similar or unusual
wording, expected bidders failing to appear, lowest bidders declining
contracts, prices falling when new or infrequent bidders enter, and winners
subsequently subcontracting to firms that lost. Procurement professionals are
typically the first to connect these signals because they alone hold tender
submissions, evaluation records, and award histories across successive
competitions.
Detection must
remain evidence-led throughout. A suspicious price, withdrawal, shared phrase
or subcontracting arrangement can have a legitimate explanation, so records
should capture facts rather than conclusions. Where concerns accumulate, legal,
governance, or counter-fraud procedures should be engaged, and credible
suspicions of cartel conduct should be reported to the CMA, which since 2023
has offered financial rewards of up to £250,000 to individuals whose
information leads to a successful investigation.
Suspicious Pricing Patterns
Pricing is one of
the clearest places to look for signs that supposedly independent bids may not
reflect genuine competition. The OECD’s 2025 Guidelines for Fighting Bid
Rigging in Public Procurement identify unexplained identical price increases,
discounts that vanish without cause, repetitive price differences and unusually
large gaps between winning and losing bids as warning signs. None alone
establishes collusion, but repeated anomalies across comparable procurements
justify closer examination of bidder behaviour and market conditions.
Identical or
near-identical prices deserve attention when the same suppliers previously
priced differently, or when varying costs, specifications and commercial
circumstances should have produced variation. A cluster of bids separated by
unusually small or mathematically regular margins can suggest coordination
rather than independent calculation. Teams should compare unit rates,
percentage differences and historical bids while weighing legitimate
explanations such as common input costs, regulated prices or highly
standardised products.
Consistently high
losing bids can indicate cover pricing, in which suppliers submit deliberately
uncompetitive tenders to create the appearance of competition while allowing an
agreed bidder to win. This was central to the Office of Fair Trading’s 2009 construction
case, in which 103 firms were fined a total of £129.2 million for bid rigging
across 199 tenders between 2000 and 2006, mostly through cover pricing and
related collusive practices.
A sudden price
reduction when a new or infrequent supplier enters can also be revealing. The
OECD notes that a significant price decline following such entry may signal
that an outsider has disrupted an established cartel. Comparing prices before
and after changes in bidder participation can expose timing that warrants
investigation, even though falling prices may equally reflect ordinary
competition, spare capacity or shifting input costs.
Identical Pricing Errors Across
Different Bids
Identical errors
across supposedly independent bids can be more revealing than identical prices,
because genuine competitors normally prepare calculations, documents and
spreadsheets separately. The OECD’s 2025 detection guidance lists identical
miscalculations, incorrect numbering and matching mistakes in bids from
different companies as warning signs. An arithmetic slip, duplicated decimal
error or unusual formula can indicate common preparation or copying, though
innocent explanations must still be tested.
The significance
turns on the nature of the mistake. Two suppliers applying the same published
tax rate or rounding convention is unremarkable. Two independent bidders
reproducing the same incorrect multiplication, transposed figure or obscure
spreadsheet formula is much harder to explain by coincidence. Reviewers should
first check whether the error originates in the contracting authority’s own
template, since a defective formula supplied to every bidder could legitimately
generate identical results.
Spreadsheet evidence
is particularly useful because formulas expose how a price was built rather
than merely showing the final figure. Where separate bidders share an unusual
calculation sequence, hidden assumptions, cell references or an erroneous
formula, that similarity may justify scrutiny. Native electronic files should
be preserved rather than printed or converted copies, since formulas, metadata
and document properties can reveal how and when competing submissions were
actually prepared.
An error becomes
genuinely concerning when it sits alongside other anomalies. Matching
miscalculations, identical wording, similar formatting, aligned submission
timing or regular differences between bid prices together form a stronger
evidential pattern than any single feature. The OECD recommends examining
tender documents for indications that competing bids were prepared by the same
person or jointly, and teams should weigh combinations of red flags rather than
treat any mistake as conclusive on its own.
Suspiciously Similar Tender Wording
Tender submissions
should be independently prepared, so unusually similar wording can indicate
that competitors have communicated or shared material. The OECD lists identical
spelling or grammatical errors, matching document order, incorrect numbering and
similar formats as possible signs of bid rigging, while CMA guidance separately
flags bids containing similar or unusual phrasing. Teams should compare
submissions carefully when supposedly rival suppliers repeatedly use the same
distinctive language or make the same mistakes.
Similarity matters
most when it goes beyond shared industry terminology. Competing suppliers may
legitimately describe statutory requirements or technical standards in
comparable language, particularly where the contracting authority prescribed
the wording. Concern grows when several bids reproduce the same unusual phrase,
qualification, exclusion, or grammatical error that was not included in the
tender documents, since such repetition can indicate copying or prior exchange
between bidders.
Formatting can offer
further clues. Separate bidders may legitimately use similar templates, but
matching headings, typographical errors, unusual fonts, indentation, table
layouts or sequencing can point to a common source where no tender template
required them. Similarity should be weighed cumulatively across presentation
and substance rather than judged on any single feature in isolation, consistent
with OECD advice to inspect documents for signs of joint preparation.
Qualifications and
exclusions deserve particular attention because they usually reflect a bidder’s
own assessment of risk. Where ostensibly independent suppliers use identical
caveats, liability wording or exclusions from scope, teams should ask whether
normal commercial reasoning explains the overlap. Concern strengthens where the
language is uncommon, appears in the same position across bids, and coincides
with aligned prices or other suspicious bidding behaviour.
Common Document Characteristics
Tender files can
reveal similarities invisible on the printed page. The OECD’s 2025 guidance
identifies matching metadata as a possible warning sign, including documents
created by the same author, files generated at or near the same time, and bids
originating from the same IP address. Such characteristics may point to common
preparation, although shared consultants, software platforms or procurement
portals can sometimes provide a legitimate explanation for the overlap.
Spreadsheet
structure can be particularly informative because it records how a price was
built. Two bidders sharing the same formula, hidden worksheet, sequencing
convention or calculation error may warrant closer examination where the
contracting authority did not supply that structure. Similarities matter more
when they concern idiosyncratic features rather than standard functions, and
teams should preserve native files, since converted PDFs strip out formulas,
properties and metadata.
Metadata can reveal
software, author details and creation or modification times, depending on how a
file was generated. The OECD specifically recognises matching metadata as a
warning sign. However, it is not inherently reliable evidence of collusion on
its own: shared advisers, group companies or reused templates can create
legitimate similarities. It should support a wider evidential picture rather
than determine conclusions in isolation.
Common presentation
quirks can also matter: repeated misspellings, unusual pagination, identical
chart styles, matching comments or unexplained worksheet names may indicate a
shared origin, particularly where several such features appear together and cannot
be traced to the authority’s own template. Reviewers should compare both
visible content and underlying file structure before deciding whether
escalation is justified.
Electronic evidence
needs careful handling once concerns arise. Original files should be retained
without alteration, along with submission records, timestamps, and
correspondence, to protect the integrity of any subsequent internal review or
CMA investigation. Editing source documents for analysis can alter metadata, so
working copies should be examined separately while originals remain preserved
within the organisation’s controlled records system.
Unexpected Bid Withdrawals
Unexpected
withdrawals can indicate bid suppression, which the CMA describes as an
arrangement in which one or more firms agree not to bid or to withdraw a bid,
thereby clearing a route for another participant to secure the contract. The
OECD similarly flags suppliers that unexpectedly or frequently withdraw
submitted bids. Repeated withdrawals deserve particular attention where the
bidder would ordinarily have had credible reasons to compete through to award.
A single withdrawal
may well be legitimate: capacity constraints, revised risk assessments, pricing
errors, loss of key personnel or competing commitments can all make continued
participation unattractive. Concern grows when the same supplier repeatedly withdraws
from desirable opportunities, does so shortly before award, or keeps bidding
elsewhere under comparable conditions. Teams should record the reasons given
and test whether those explanations match the commercial circumstances.
Patterns across
suppliers can be more revealing than any single withdrawal. If Supplier A
withdraws when Supplier B is best placed to win, while Supplier B later
withdraws from a tender favouring Supplier A, the sequence may warrant
examination for rotation or suppression. Suspicion strengthens if withdrawn
suppliers later receive subcontracts, if expected bidders repeatedly stay away,
or if withdrawals coincide with unusual price movements across a series of
tenders.
The Winning Bidder Subcontracting to
a Losing Bidder
Subcontracting is
common and often economically efficient, allowing a prime contractor to draw in
specialist capability, local coverage or additional capacity it does not hold
internally. Concern arises when a successful bidder unexpectedly subcontracts substantial
work to a competitor that submitted a losing bid, since the OECD identifies
this pattern as a possible warning sign: a subcontract can serve as
compensation for agreeing not to compete.
Commercial context
matters. A losing bidder may be the most capable specialist for a discrete
package, or hold scarce equipment or accreditation needed for delivery, all of
which can explain subcontracting without any collusion. Suspicion increases
where the losing bidder was previously capable of delivering the whole
contract, its bid appeared deliberately uncompetitive, or the subcontract was
foreseeable but concealed during tendering without a convincing operational
rationale.
OECD guidance
explains that bid-rigging cartels may compensate participants who lose or
refrain from bidding by awarding them subcontracts or supply arrangements once
the designated winner secures the work, helping conspirators share cartel
profits and discouraging members from cheating on the agreement. Teams should
therefore compare declared supply chains against post-award subcontracting,
especially where the same competitors repeatedly exchange work after losing
tenders.
Historical UK
enforcement shows precisely why compensation deserves scrutiny. In the OFT’s
2009 construction case, alongside the 199 rigged tenders, the OFT found six
instances in which successful bidders made agreed payments to unsuccessful
bidders, ranging from £2,500 to £60,000 and facilitated by false invoices.
Although payments rather than subcontracts, they demonstrate concretely how
losing participants can be rewarded for supporting a collusive scheme.
Rotation of Contract Awards
Bid rotation occurs
when competitors agree to take turns winning contracts rather than compete
independently for each opportunity. The arrangement may follow a simple
sequence, such as Supplier A, then Supplier B, then Supplier C, or allocate
contracts by value, volume or market share. The OECD recognises rotation as a
classic form of bid rigging and warns procurement officials to watch for
companies that repeatedly appear to take turns winning.
A rotating sequence
is suspicious when losing bids appear designed not to win: prices are unusually
high, qualifications are needlessly restrictive, or submissions are compliant
yet consistently weak. Cover bids can support rotation by preserving the
appearance of competition while protecting the agreed winner. The Public Sector
Fraud Authority describes bid rotation as firms agreeing to take turns
submitting the most attractive bid so that each obtains a share of the
available market.
Rotation rarely
becomes obvious from a single procurement because each award can look
defensible viewed in isolation. A team may see three compliant bids, evaluate
them correctly and award to the highest-scoring supplier without detecting
anything unusual at all. The pattern only becomes visible when results are
compared over time, when win sequences, bidder combinations, price gaps and
participation rates reveal a regularity that ordinary commercial rivalry would
not readily produce.
Patterns should
still be tested against legitimate explanations. Different suppliers may have
genuinely different capacities, specialist expertise, or geographic strengths
that lead to awards alternating without coordination. At the same time,
framework call-offs, seasonal workload, and contract size can influence who
bids competitively at any given time. Concern strengthens where rotation
remains unusually orderly despite changing specifications and market
conditions, particularly if losing suppliers rarely challenge the apparent
turn.
Teams should retain
enough data to identify recurring sequences rather than relying solely on
individual evaluation files, capturing bidder identity, price, score,
withdrawal, contract value, location, incumbency, subcontractors and award
outcome. The OECD recommends examining bidding patterns and the frequency of
wins and losses; where apparent rotation coincides with cover bids, withdrawals
or suspicious communications, the combined evidence provides a stronger basis
for escalation.
Geographical Patterns in Tender
Results
Geographical
allocation is another recognised form of bid rigging, in which competitors
agree that each will dominate particular territories and avoid meaningful
competition in areas allocated to others. The OECD describes market allocation
as agreements not to compete for particular customers, geographic areas, bids,
goods, services or works. Teams may detect concerns when suppliers consistently
win in specific territories despite having the capability to compete in
neighbouring areas for comparable contracts.
The pattern can
appear through participation as much as through awards. A supplier might bid
aggressively in one county while declining invitations or submitting weak,
high-priced bids just across the boundary, with a competitor behaving in
exactly the opposite way. Repetition matters: one distant project may involve
high mobilisation costs, but a persistent geographic division between capable
competitors is harder to explain where travel distances and delivery conditions
remain comparable.
Pricing can help
distinguish genuine geographic cost differences from suspicious allocation.
Transport, labour availability, depot locations, congestion, local wage rates
and mobilisation requirements can legitimately make one territory more
expensive than another. Analysts should compare price differentials against
measurable cost drivers rather than assume that regional variation indicates
collusion, with concern rising when prices change abruptly at territorial
boundaries or when bidders reverse their competitiveness upon entering areas
routinely won by particular rivals.
The OECD’s detection
guidance identifies geographic allocation of winning tenders as a warning sign,
including cases where particular bidders win only in specific areas. Mapping
awards, bid participation, and price rankings over several years can expose
boundaries that are invisible in spreadsheets, particularly where the same
firms repeatedly avoid one another; analysis should include unsuccessful bids,
as cover pricing can conceal an underlying territorial agreement.
Geographic patterns
should always be weighed against market structure and operational reality.
Suppliers with local depots, specialist licences or shorter travel distances
may hold genuine regional advantages, and teams should document these
explanations before escalating. Where boundaries remain stable despite new
contracts, changing costs and sufficient supplier capability, the pattern
becomes more significant, particularly alongside reciprocal non-entry, cover
bids or statements suggesting a territorial understanding.
The Same Suppliers Always Winning
the Same Customers
Customer allocation
operates like geographic allocation, except competitors divide buyers rather
than territories. One supplier may repeatedly win contracts from Customer A
while another dominates Customer B, each avoiding meaningful competition for
the other’s business. The OECD identifies agreements not to compete for certain
customers as a form of market allocation; long-term customer loyalty is not
inherently suspicious, but reciprocal patterns among capable competitors
warrant closer analysis.
Normal competitive
advantage can also produce persistent winners. Incumbents may understand an
organisation’s estate and systems better than rivals, while strong performance
or lower logistics costs can support repeated success on entirely legitimate
grounds. Teams should therefore ask whether observed outcomes reflect
measurable advantages, with concern increasing where other capable suppliers
consistently submit token bids, decline opportunities, or price themselves out
of particular customers’ work while competing aggressively elsewhere.
Customer allocation
need not be confined to construction. In 2018, following a tip-off, the CMA
found that two of the UK’s largest suppliers of barbecue charcoal had shared
out customers and rigged bids between themselves, and fined the pair £3.4
million in total, a figure reduced by 20% because both firms admitted the
infringement and cooperated with the investigation. The case shows that
customer allocation can arise in ordinary consumer-facing supply chains, not
only major infrastructure contracts.
The strongest
evidence often lies in reciprocity. Where Supplier A rarely competes seriously
for Customer B while Supplier B behaves similarly toward Customer A, outcomes
may indicate an understanding to respect established accounts, since OECD
guidance notes that market-allocation participants may refrain from bidding or
submit cover bids for customers assigned to a fellow conspirator. Behaviour
repeated across several buyers can reveal a structure that any single award
decision would not expose.
Teams can test
customer-allocation concerns by comparing bidder participation, win rates,
price rankings, and incumbency across organisations, where lawful data access
permits, and assessing these over time and against contract characteristics,
because customer specialisation can be entirely legitimate. Suspicion becomes
credible when loyalty coincides with reciprocal avoidance, deliberately weak
bids, rotation, unexplained subcontracting or evidence of direct communication
between competitors.
Suspicious Bid Timing and Behaviour
Bid timing can
reveal behaviour that prices alone do not. The CMA identifies bids received at
the same time, the sudden disappearance of expected discounts, and other
last-minute changes as possible warning signs. Teams should record submission
times, withdrawals, amendments, and bidder enquiries rather than treating them
as incidental details, since repeated timing patterns involving the same
suppliers can become significant when they coincide with unusual pricing or
outcomes.
Last-minute
withdrawals deserve particular scrutiny where a supplier appeared capable and
commercially interested throughout the process. A legitimate bidder may
withdraw for genuine reasons, but repeated late withdrawals can also indicate
bid suppression, as the OECD lists the unexpected or frequent withdrawal of
submitted bids as a warning sign, particularly where regular suppliers continue
to compete for comparable opportunities elsewhere without an obvious
explanation.
Submission sequences
can also become informative when the same suppliers repeatedly tender in a
strikingly consistent order or at similar times. Timing alone proves nothing,
since procurement portals and shared deadlines naturally cluster submissions.
Concern rises when timing aligns with other indicators, such as a single bidder
consistently submitting after competitors, late price changes following market
participation, or withdrawals that clear a path for the expected winner.
Attempts to discover
who else is bidding can also deserve attention. The OECD lists a company’s
attempt to determine the identities of other bidders as suspicious,
particularly when accompanied by meetings, shared enquiries or other evidence
of coordination. Procurement teams should distinguish ordinary market curiosity
from persistent efforts to obtain non-public bidder information, since apparent
advance knowledge of participation or likely outcomes materially strengthens
the case for closer examination.
Statements That Reveal Too Much
What individual
suppliers say can sometimes reveal more than their formal bids. The OECD lists
references to agreements among bidders, statements that territories or
customers belong to another supplier, and advance non-public knowledge of a
competitor’s prices as warning signs. Procurement professionals should record
the exact words, date, context, and participants because an apparently casual
remark can become important when weighed alongside pricing, participation, and
award patterns.
A comment such as “it
is their turn” can be particularly significant because bid rotation involves
competitors agreeing to take turns winning. The phrase does not prove an
unlawful agreement on its own, since staff may use informal language to
describe an expected result, but when it accompanies a recurring sequence of
winners and deliberately weak losing bids, it makes an otherwise ambiguous
pattern considerably more suspicious.
A remark that
another supplier “wanted this one” may be innocuous where competitors
understand one another’s specialisms. It becomes more concerning when the
speaker appears to know a rival’s precise intentions before award, or implies
that contracts have been informally divided, consistent with OECD guidance
treating statements about territory or customer ownership as a warning sign of
possible market allocation between competitors.
Beyond the civil
regime, statements suggesting a deliberate agreement can also point towards
individual criminal liability. Under section 188 of the Enterprise Act 2002, an
individual who agrees with others to fix prices, share customers or rig bids
commits the cartel offence, punishable on conviction by up to five years’
imprisonment and an unlimited fine; three individuals received custodial
sentences of up to two-and-a-half years in the 2008 Marine Hoses prosecution.
Since 2014, the offence has no longer required proof of dishonesty, thereby widening
its reach.
Knowledge of another
bidder’s pre-publication price is particularly difficult to reconcile with
independent bidding when that price was confidential. The OECD expressly
identifies advance non-public knowledge of a competitor’s pricing as
suspicious. An isolated comment may arise from subcontracting discussions or
accidental disclosure, so context matters, but concern is heightened when the
knowledge is precise, unexplained, and accompanied by other signs that
competitors communicated it before submission.
Looking Across Procurements Rather
Than at One Tender
A single tender
often provides too little context to expose collusion. Three compliant bids and
a defensible award can appear entirely competitive even where suppliers
coordinated behind the scenes. The OECD therefore recommends examining bidding
patterns and the frequency with which firms win or lose, since a clearer
picture emerges once several years of awards, unsuccessful bids, withdrawals
and subcontracting relationships are analysed together rather than reviewed in
isolation.
Longitudinal
analysis can reveal patterns that individual evaluation panels cannot see:
Supplier A may repeatedly win one customer while Supplier B wins another, both often
submitting losing bids to preserve the appearance of competition; or three
suppliers may rotate awards while strategically withdrawing. Mapping bidder
combinations, pricing gaps and participation across many procurements can
surface regularities that would be statistically or commercially difficult to
spot in any single competition.
Historical data also
helps distinguish collusion from legitimate commercial behaviour. A high price
in one tender may reflect genuine capacity constraints or risk, while a
withdrawal may result from workload; if the same behaviour recurs whenever a
particular competitor participates, however, the innocent explanation becomes
progressively less persuasive, which is why the OECD recommends retaining
winning and losing bids, correspondence and records of suspicious behaviour
within controlled information systems.
The clearest UK
illustration of the value of looking across tenders is the CMA’s 2023 finding
against ten construction firms — Brown and Mason, Cantillon, Clifford Devlin,
DSM, Erith, John F Hunt, Keltbray, McGee, Scudder and Squibb — which
collectively rigged bids for 19 demolition and asbestos-removal contracts worth
over £150 million between January 2013 and June 2018, affecting sites including
the Metropolitan Police Training College, Bow Street Magistrates’ Court,
Selfridges and Oxford University. The CMA imposed fines of £59,334,957 and
secured the disqualification of three company directors.
Analysis across
procurements should still avoid assuming that repetition equals collusion.
Incumbency, regional depots, specialist accreditation and genuine supplier
capacity can legitimately produce recurring winners and bidder combinations.
The purpose is to identify patterns that require explanation, not to
manufacture a finding of guilt. Where several independent indicators converge,
teams should preserve the evidence, seek specialist advice, or report serious
suspicions to the CMA rather than confront suppliers directly.
Using Data Analytics to Detect
Collusion
Data analytics
allows procurement teams to test patterns systematically rather than rely on
intuition. Useful measures include bid dispersion, participation rates, win
rates, price rankings, geographic distribution, withdrawal frequency, recurring
supplier combinations and subcontracting relationships. Correlation analysis
can identify prices that move together unusually closely, while anomaly
detection highlights departures from historical behaviour; the objective is to
prioritise procurements for human review, not to automate determinations of
guilt.
Bid dispersion can
show whether competitors’ prices cluster unusually tightly or maintain
recurring gaps, while participation analysis can reveal suppliers that
repeatedly appear together, avoid one another, or enter only when particular
rivals are absent. Win-rate analysis can identify improbable rotation or
dominance, and geographic mapping can expose territorial boundaries; each
measure needs commercial context, since transport costs, capacity and
procurement design can all produce patterns that resemble collusion without any
unlawful agreement.
The CMA has steadily
built data science into cartel detection since launching its Screening for
Cartels tool with the analytics firm Spend Network in December 2017, giving
procurers free software to scan tender data for algorithmic signs of unusual
bidder behaviour. Its 2026 to 2027 Annual Plan takes this further, confirming
that anti-competitive bid rigging can inflate prices by 20% or more and
committing the authority to use AI and other data-science tools to scan bidding
data and identify illegal activity at scale.
Analytics is
strongest when quantitative signals are combined with documentary and
behavioural evidence. A pricing correlation becomes more significant when
paired with identical errors, unusual wording, suspicious withdrawals, shared
metadata or statements revealing foreknowledge. Teams should establish
baselines, monitor changes over time and investigate anomalies proportionately,
recognising that data models can identify where scrutiny is warranted, but
legal conclusions require sufficient evidence and commercial context rather
than algorithmic scores alone.
Red Flags Are Evidence to
Investigate, Not Proof of Guilt
Red flags are
prompts for investigation, not findings of guilt. The OECD expressly cautions
that suspicious bidding patterns, statements and behaviour should not be
treated as proof of bid rigging, since innocent explanations may exist: a
supplier may quote highly because it assesses risk differently, decline work
because capacity is constrained, or withdraw because circumstances genuinely
change. Teams should test for anomalies objectively before concluding that
collusion or misconduct occurred.
That safeguard
matters because procurement data naturally contains coincidence. Similar prices
can result from common input costs or regulated charges, repeated winners may
reflect incumbency or genuine expertise, and identical document features can
originate from authority templates or shared software. The evidential question
is therefore whether several independent indicators converge, recur across
procurements, and resist a credible commercial explanation, rather than whether
a single suspicious feature appears.
The stakes for
getting this right have risen under the Procurement Act 2023. A CMA finding
that a supplier participated in cartel activity can trigger a mandatory
exclusion ground where statutory conditions are met. Suppliers may also be
considered for the central debarment list through the ministerial process.
Debarment can prevent participation in covered procurements for up to five
years, subject to the Act’s rules, including self-cleaning and relevant
exceptions.
Where several red
flags create serious suspicion, teams should preserve records, avoid alerting
suspected bidders, and seek specialist advice; the OECD recommends checking
serious suspicions with the relevant competition authority, which in the United
Kingdom is the CMA. That division of labour protects due process: procurement
professionals identify and document anomalies, while the CMA investigates
whether the evidence establishes unlawful coordination under the Competition
Act 1998.
Designing Procurement to Promote
Genuine Competition
Procurement design
can make collusion either easier or harder. OECD guidance recommends maximising
participation by genuinely competing bidders through clear specifications, open
tendering where possible, and conditions of participation that are relevant and
proportionate. Unnecessary turnover thresholds, excessive experience demands or
disproportionate guarantees can exclude credible entrants and leave a smaller,
more predictable supplier group that is easier to coordinate.
Contract structure
also shapes competitive intensity. Large aggregated contracts may attract
capable suppliers but exclude smaller competitors, while excessive
fragmentation can create convenient parcels for cartel members to divide
between themselves. The OECD recommends carefully weighing aggregation and
disaggregation, allowing bidding on appropriate lots while avoiding structures
that mirror the number of likely bidders, thereby inviting informal allocation.
UK procurement law
reinforces attention to participation barriers. Under section 12 of the
Procurement Act 2023, contracting authorities must have regard to barriers
faced by small and medium-sized enterprises and consider whether those barriers
can be removed or reduced. For these purposes, an SME has fewer than 250 staff
and either turnover of £44 million or less, or a balance-sheet total of £38
million or less, subject to ownership considerations.
Understanding the Market Before
Tendering
Effective prevention
starts before the tender is drafted. The OECD recommends understanding the
relevant market, potential suppliers, recent industry trends, past tenders and
alternative sources of supply. Teams should know how many suppliers could realistically
perform the requirement, not merely how many names appear on an approved list;
a market with ten registered suppliers may still exhibit weak competition if
only three genuinely have the capacity to deliver.
Ownership structures
can materially change that picture. Two bidders with different trading names
may belong to the same corporate group, and joint ventures, parent companies or
commercial ties can affect whether apparently separate bids represent genuinely
independent competitive pressure. OECD guidance recommends requiring bidders to
disclose corporate structure and beneficial ownership, together with relevant
ties to other companies, joint contractors and subcontractors connected with
the particular tender.
Capacity and
geographic coverage should be tested realistically. A national supplier may
lack operational resources in one region, while a smaller local firm may have
stronger delivery capabilities there; depot locations, labour availability,
specialist equipment, and mobilisation times can all influence competitive
reach. Understanding these factors helps teams distinguish legitimate regional
pricing from suspicious territorial allocation, and prevents tender
requirements from inadvertently excluding suppliers capable of delivering well.
Barriers to entry
deserve equal attention because collusion is easier where new competitors
rarely enter. The OECD identifies little or no entry as a market characteristic
that can facilitate bid rigging, particularly where entry is costly or slow.
Teams should examine accreditation, insurance, capital investment, incumbent
data access and mobilisation periods to determine whether procurement choices
unnecessarily reinforce those barriers for credible new entrants.
Subcontracting
relationships can reveal both capability and competitive risk. A supplier may
depend on a rival for specialist equipment, labour or inputs, creating
commercial links that can explain pricing or participation patterns without
collusion. OECD guidance recommends understanding ties between bidders and
requiring disclosure of joint contractors and subcontractors, so market
intelligence maps who can deliver independently and where repeated supply-chain
relationships could, in practice, reduce genuine competition.
Certificates of Independent Bidding
and Non-Collusion Clauses
Certificates of
independent bidding require suppliers to confirm that their tenders are genuine
and non-collusive. The OECD Recommendation on Fighting Bid Rigging supports
signed attestations stating that a bid is genuine, non-collusive and submitted
with an intention to accept the contract if awarded. Tender documents may also
require disclosure of communications with competitors, making expectations
explicit before the authority evaluates bids.
Their value lies in
deterrence and accountability rather than detection by themselves. A signed
declaration makes it harder for individuals to claim that independence
requirements were unclear, and creates a documentary record against which later
evidence can be tested. Non-collusion clauses reinforce the same message by
prohibiting coordination and setting out contractual consequences, provided
they are drafted consistently with applicable procurement and competition law.
Certificates cannot
guarantee independent bidding, since a cartel participant may sign falsely.
Their effectiveness, therefore, depends on enforcement, proportionate tender
controls, and continuing scrutiny of behaviour and data. OECD guidance also
recommends warning bidders about the scale of sanctions for bid rigging and
explaining reporting mechanisms; combined with training and clear escalation
routes, declarations signal that the authority understands the risk of
collusion and is prepared to challenge suspicious conduct.
Protecting Commercially Sensitive
Information
Commercially
sensitive information should be controlled carefully, because excessive
transparency can make collusion easier to organise and monitor. The OECD warns
authorities to consider carefully what information is disclosed during bidding
and after award. Revealing detailed losing prices, bidder identities or
strategic information can help competitors understand one another’s behaviour,
detect deviations from a cartel arrangement, and adjust future bids with
greater confidence.
Teams should
distinguish necessary transparency from unnecessary commercial disclosure.
Suppliers need enough information to understand requirements, evaluation
methods, and contractual obligations, but do not normally have access to
competitors’ confidential pricing strategies or bidding intentions. The OECD
specifically recommends avoiding disclosure of bidder identities to one another
where possible, since limiting unnecessary information exchange reduces
competitors’ ability to coordinate conduct during or between tender exercises.
Information released
after award also requires judgement. Publishing enough detail to explain the
outcome and meet transparency obligations under the Procurement Act 2023 does
not require unrestricted disclosure of commercially sensitive material, since the
OECD cautions that tender results can facilitate collusion if they reveal
information competitors can use to monitor one another. Disclosure rules should
therefore balance transparency, accountability and confidentiality rather than
assume that more published information automatically improves competition.
Communication
channels should also be structured to prevent suppliers learning about
competitors indirectly. Clarification questions can be anonymised where
appropriate, bidder meetings can avoid unnecessary disclosure of attendance,
and commercially sensitive responses should not be circulated. Maintaining
records of what information has been shared, and with whom, protects fairness
while reducing suppliers’ ability to infer competitors’ identities, pricing
approaches or strategic intentions before award.
Managing Preliminary Market
Engagement
Preliminary market
engagement can improve procurement design by testing specifications, capacity
and likely supplier interest before competition begins. Under section 16 of the
Procurement Act 2023, contracting authorities may engage suppliers for purposes
including developing requirements and preparing tender documents, provided they
take steps to ensure that participating suppliers are not unfairly advantaged
and that competition is not distorted as a result.
Market engagement
should seek intelligence without becoming a forum for competitors to exchange
sensitive information. Group events can usefully explain requirements or
identify barriers, but discussion should be carefully structured; suppliers
should not be invited to disclose future prices, margins or bidding plans in
front of rivals. Bilateral engagement may be preferable where genuinely
sensitive matters need exploration, provided all participants are treated
fairly overall.
The Procurement Act
2023 also creates transparency requirements around this stage. Under section
17, an authority that undertakes preliminary market engagement must either
publish a preliminary market engagement notice before its tender notice, or
explain in the tender notice why none was published. Government guidance states
that such notices support a level playing field and can attract new entrants,
strengthening rather than narrowing participation.
Information obtained
from one supplier should never be allowed to shape a procurement secretly in
that supplier’s favour. Government guidance confirms that information gathered
during preliminary market engagement can be shared with the wider market, and
that adequate tender timescales can prevent unfair advantage. Specifications
should reflect organisational needs rather than a single incumbent’s
proprietary solution, and records should explain decisions sufficiently to
demonstrate fairness where engagement materially influenced requirements.
Broad participation
reduces both procurement risk and collusion risk. Government guidance
encourages engagement with a range of suppliers, noting that market engagement
can particularly help new entrants and SMEs understand opportunities. Teams can
invite input from incumbents, challengers, trade bodies, and potential
substitutes while avoiding unnecessary disclosure among them, since diverse
input makes tender design less dependent on a small, repeatedly consulted group
of suppliers.
Preliminary market
engagement should be documented as carefully as the competition itself. Records
should identify participants, subjects discussed, information received and any
measures taken to neutralise advantage, with conflicts of interest identified
and mitigated under the Procurement Act’s conflicts regime. Good records allow
later reviewers to distinguish legitimate market intelligence from supplier
influence, and help demonstrate that engagement increased understanding without
compromising equal treatment between bidders.
Maintaining Competitive Tension
Competitive tension
depends on suppliers believing that contracts must genuinely be won rather than
informally allocated. Teams should avoid practices that make opportunities
predictable, such as repeatedly using identical contract sizes, tender dates, lots
and supplier lists. OECD guidance recommends reducing predictability, because
recurring, formulaic procurement can help cartel members divide opportunities
and monitor one another’s compliance with an agreement.
Future contract
allocation should also remain genuinely contestable. Frameworks, dynamic
markets and repeat procurements should not be managed so predictably that
incumbents can assume work will return to them. Competitive tension weakens
when suppliers believe outcomes are predetermined by geography or informal
rotation, which teams can challenge by refreshing markets, reducing barriers,
widening participation and reconsidering packaging where evidence shows
existing structures discourage serious bids.
Evaluation design
can either sustain or weaken competitive pressure. Criteria should be clear,
proportionate and connected to the requirement, but should not unnecessarily
favour incumbents or set conditions only a familiar supplier can satisfy. The
OECD recommends selection and award criteria that improve the intensity of
competition, so teams should regularly test whether qualification thresholds or
technical specifications exclude credible challengers without a defensible
procurement rationale.
Maintaining
competitive tension does not mean changing procurement rules unpredictably or
withholding information suppliers legitimately need. Fair competition requires
published requirements, transparent evaluation methods and equal access to
material information; the objective is to prevent competitors from predicting
one another’s conduct or assuming future market shares. Process consistency
combined with genuine uncertainty about who will win preserves rivalry without
compromising procedural fairness.
Training Procurement Teams to
Recognise Collusion
Training is
essential because procurement professionals are often best placed to detect
suspicious bidding patterns before competition authorities become involved. The
OECD recommends training covering competition-law concepts, bid-rigging
detection, data analysis, sanctions, leniency arrangements, whistleblowing
channels and how to contact the competition authority. Practical training
should enable staff to recognise cover bids, suppression, rotation, allocation
and suspicious statements without assuming that red flags prove collusion.
Competition-law
awareness should extend beyond procurement teams to commercial managers,
contract managers, finance staff and internal auditors, who may each hold
information that only becomes significant when combined. A contract manager may
notice unexplained subcontracting while finance identifies unusual invoice
relationships and procurement sees rotating awards; shared training and
escalation routes help organisations connect those observations before
suspicious patterns remain unnoticed for years.
Scenario-based
training is valuable because bid rigging rarely announces itself through
explicit confession. Teams can practise identifying identical pricing errors,
suspicious withdrawals, common metadata, geographic allocation and remarks such
as “it is their turn”, including innocent explanations. Hence, staff learn to
distinguish indicators from proof. This reduces both under-reaction and
unsupported accusations, reinforcing careful investigation and referral to
legal, fraud or competition specialists when concerns become credible.
Training should be
refreshed regularly because markets, procurement methods and detection tools
all change. The OECD’s 2025 guidance encourages closer relationships between
competition and procurement authorities and regular training on cartel
detection. Organisations should build bid-rigging awareness into induction,
procurement governance and contract management development, covering what to
record, what not to disclose, when to escalate, and why suspected suppliers
should not be alerted directly.
Summary – Detecting the Pattern,
Protecting Competition
Bid rigging rarely
reveals itself through one dramatic warning sign. It is more often detected
through patterns: unusual prices, repeated losing bids, identical errors,
shared wording, suspicious withdrawals, rotating awards or unexplained
geographic divisions. Procurement professionals are well placed to notice these
signals because they compare suppliers across competitions. Their task is not
to presume guilt, but to recognise anomalies, preserve evidence and ensure
credible concerns receive appropriate examination.
Patterns become more
meaningful when several procurements are considered together. A single high
bid, withdrawal or subcontract may have an innocent commercial explanation,
whereas recurring behaviour involving the same suppliers can warrant closer
scrutiny. Historical award data, participation rates, bid dispersion, supplier
combinations, and geographic outcomes can reveal relationships that are
invisible within a single tender. Data analytics strengthens that capability by
helping procurement teams identify unusual correlations and prioritise review
cases.
Behavioural evidence
can be equally important. Statements suggesting that a contract belongs to
another supplier, that it is someone else’s turn, or that a bidder was not
expected to win may indicate coordination when supported by other facts.
Similar documents, shared metadata or unexpected knowledge of competitors can
reinforce concern. Such indicators should be recorded accurately and assessed
collectively because no isolated comment, spreadsheet feature or decision
establishes unlawful collusion.
Prevention begins
with procurement design. Wider market participation, proportionate entry
requirements, sensible lotting and reduced predictability can make collusion
harder to organise and sustain. Authorities should understand supplier
ownership, capacity, geographic coverage, subcontracting relationships and
barriers to entry before tendering. Preliminary market engagement can improve
specifications and attract challengers, but it must be structured so
competitors do not exchange pricing intentions, capacity plans or commercially
sensitive information with one another.
Information control
and competitive tension remain essential throughout the process. Suppliers
require enough information to bid fairly, but unnecessary disclosure of bidder
identities, losing prices or strategic information can help competitors
coordinate or monitor cartel arrangements. Independent bidding certificates and
non-collusion clauses can reinforce expectations and accountability, although
they cannot replace scrutiny. Procurement structures should keep opportunities
genuinely contestable rather than allowing incumbents to predict allocation,
rivals or likely outcomes.
Ultimately,
effective protection against bid rigging depends on informed procurement
professionals supported by sound governance. Training should cover suppression,
rotation, market allocation, suspicious communications and appropriate
escalation. Red flags should trigger questions rather than accusations, with
records preserved and serious concerns referred through legal or competition
channels. Genuine competition is strengthened when procurement teams combine
commercial awareness, disciplined analysis and careful tender design with a
working understanding of competition law.
Additional articles can be found at Procurement Made Easy. This site looks at procurement issues to assist organisations and people in increasing the quality, efficiency, and effectiveness of their product and service supply to the customers' delight. ©️ Procurement Made Easy. All rights reserved.
Further Reading
- OECD (2025), OECD Guidelines for Fighting Bid Rigging in Public Procurement (2025 Update), OECD Publishing, Paris — oecd.org
- Competition and Markets Authority, Bid-rigging: advice and tools for public sector procurers (collection) — gov.uk
- Competition and Markets Authority, Case study: lessons from the construction bid-rigging investigation — gov.uk
- Competition Act 1998, Chapter I — The prohibition (section 2) — legislation.gov.uk
- Procurement Act 2023 — legislation.gov.uk
- Competition and Markets Authority, Annual Plan 2026 to 2027 — gov.uk
