How CMA and DMCC rules affect attribution claims in UK advertising

What to take away

What the CMA expects when an advertiser attributes results to marketing

The Competition and Markets Authority is the UK's competition and consumer law regulator. It expects any performance claim you publish to a consumer to be true, clear and capable of proof. That applies whether the claim sits in a pitch deck, a landing page or a paid ad.

A claim that a campaign delivered a return, a lift or a set number of conversions is a commercial claim. The Competition and Markets Authority - GOV.UK page collects the guidance and casework that show how it reads those claims in practice.

Attribution claims are treated as outcome claims. If you say a channel produced revenue, the CMA's starting point is that you can show the link between the spend and the result.

Last-click numbers, platform-reported conversions and modelled figures are all evidence, but each carries limits you should state. The regulator does not require a particular model. It requires that the model you used supports the claim you made.

The CMA also looks at the impression the whole claim creates, not just the literal words. A headline that says a campaign doubled return on ad spend, with a footnote saying the figure is modelled, may still mislead.

The test is what the average consumer takes away. If the qualification changes the meaning, it belongs in the claim, not below it.

A worked example shows the difference. An agency publishes a case study saying a campaign delivered a 4:1 return. The evidence is platform-reported revenue divided by platform spend over 30 days, with no holdout.

The claim is defensible only if it says attributed return, names the platform and states the window. Reworded as incremental return, it becomes an outcome claim the evidence cannot support. The fix is to change the wording or run a test, not to add a footnote.

Evidence must exist before publication and be contemporaneous. Records created after a complaint carry less weight than records made when the claim was published. Keep the raw data, the query, the model version and the person who signed the claim off. That file is what you hand over if the CMA asks.

For a practical pre-publication route, see checking an attribution-based advertising claim.

The CMA can seek undertakings, impose fines and require corrections. It can also name businesses in its casework, which affects reputation as much as revenue. In 2022 it fined Compare the Market £17.9 million for breaching a market investigation order and published the decision.

The Digital Markets, Competition and Consumers Act 2024 in practice

The Digital Markets, Competition and Consumers Act 2024 is the statutory basis for much of the CMA's consumer enforcement. It replaced the older consumer regime with a direct enforcement model, so the CMA can decide that a practice is unfair and act without going to court first.

For advertisers, the practical change is speed. The CMA can investigate, publish its view and impose penalties on its own authority. It can also accept undertakings and run its own redress schemes. A misleading attribution claim that once carried a slow court route now carries an administrative one.

The Act also gives the CMA powers over online choice architecture. Ranking, prominence and default settings all fall within scope. An attribution claim that is technically accurate but buried or contradicted elsewhere on the page can be caught. Where you place a claim matters as much as what it says.

Fines under the regime are set at the higher of 10 per cent of global turnover and £300,000. The exact figure depends on the breach and the business. The deterrent is the point: the cost of a weak claim can exceed the cost of the campaign that produced it.

Unfair commercial practices and the Consumer Protection Regulations 2008

Unfair commercial practices are the core prohibition. A practice is unfair if it contravenes professional diligence and materially distorts the consumer's behaviour. Misleading actions and omissions both count. The Consumer Protection from Unfair Trading Regulations 2008 set out the original framework the CMA still applies.

A misleading action includes a false statement, or one that deceives the average consumer, even if the statement is literally true. An attribution claim that implies a causal result where only correlation exists can fall here. So can a claim that omits the fact that a result was modelled or measured over a short window.

A misleading omission is failing to give information the consumer needs to make an informed decision. If your attribution claim rests on a sample of one campaign or one region, that context is material. Leaving it out can make the claim misleading even when the number is accurate.

The regulations also list practices that are unfair in all circumstances. These include falsely claiming endorsements and using misleading claims about a product's results. An attribution claim built on invented or unverifiable data can reach that category.

Defences exist but are narrow. Showing that you followed a recognised code, or that you took all reasonable precautions, may help. It does not rescue a claim you cannot evidence. The burden sits with the advertiser.

What the ASA advertising codes require for substantiation

The Advertising Standards Authority writes and enforces the UK advertising codes. The codes require that claims are honest, decent and truthful, and that advertisers hold evidence before publication. The advertising code rules on misleading claims and evidence for attribution are the operative text.

Substantiation of performance claims is a documentary test. The sign-off file matters more than the final creative.

Attribution evidence must match the claim. A claim about incremental sales needs incrementality evidence, such as a holdout or a geo test. A claim about attributed sales can rest on platform or analytics data, provided the wording says attributed. The ASA reads the claim as the consumer would, so the distinction must be visible.

The ASA also expects qualifications to be clear and proximate. Small print that contradicts the headline is not a defence. If the model, window or sample changes the meaning, put it in the claim. The same principle applies across paid search, social, display and email.

Complaints are usually resolved by amending or withdrawing the ad, but the ASA can refer persistent offenders to other regulators. For a wider view of how the pieces fit, see mapping UK attribution rules.

Broadcast advertising rules on performance claims

Broadcast advertising adds a clearance step. Commercials on TV and radio must be cleared before transmission, and the broadcaster or clearance body will ask for evidence. The broadcast advertising rules on substantiation of performance claims set out what that evidence must show.

Performance claims in broadcast are held to the same truthfulness standard as other media, with less room for qualification. A 30 second spot cannot carry a footnote. If a claim needs a caveat to be accurate, it usually cannot run as stated.

Clearance teams commonly ask for the source, the sample period, the method and the party that produced the figure. Platform-reported attribution is accepted when the claim is framed as platform-reported. Incremental claims need test evidence. Vague wording such as proven results invites a request for the underlying study.

Testimonials and case studies in broadcast are claims too. If a client says a campaign transformed their business, that statement needs a basis. The advertiser carries responsibility for claims made by others in its advertising.

Radio adds a timing problem. A qualifying statement can take longer to say than the claim it qualifies. Write the evidence first, then the script, so the two can be matched inside the slot.

Keep the broadcast evidence pack separate from the general analytics stack. It needs to be retrievable on the day of clearance, not reconstructed afterwards. The same pack supports any later ASA enquiry.

Where CMA, DMCC and ASA boundaries sit for attribution claims

The boundaries overlap but the triggers differ. The CMA and the Digital Markets, Competition and Consumers Act 2024 focus on consumer protection and market conduct. The ASA focuses on advertising content across media. A single attribution claim can interest both.

The CMA is more likely to act where there is a pattern of misleading conduct, a market-wide problem or significant consumer detriment. The ASA is more likely to act on a single ad following a complaint. Neither needs the other's permission, and their findings can be used by the other.

The DMCC regime strengthens the CMA's hand and shortens the route to a sanction. That makes the CMA the bigger financial risk for a deliberate or repeated misstatement. The ASA remains the faster reputational risk for a careless one.

Sector regulators can also be involved. The Information Commissioner's Office polices personal data used in tracking under UK GDPR and the Privacy and Electronic Communications Regulations. Attribution that relies on tracking must be lawful before it can be claimed.

Statistics claims can attract the Office for Statistics Regulation if they are presented as official statistics. They rarely are, but the principle holds: do not dress marketing data as official data. For a boundary map across regimes, see which UK rules may reach.

Reporting a competition or market problem to the CMA

Anyone can report a competition or market problem to the CMA. Advertisers, agencies and members of the public can submit information about misleading claims or anti-competitive conduct. The CMA publishes how to do this and what happens next.

Reports are most useful when they are specific. Give the claim, where it appeared, when it ran and why you think it is misleading. Attach the evidence you have. Anonymous reports are accepted but are harder to act on.

The CMA may open a case, add the information to existing work or take no action. It does not report back on every submission. If the issue is advertising content rather than market conduct, the ASA route is usually quicker.

Businesses can also raise concerns through their trade bodies. Collective action carries more weight than a single complaint, particularly where several advertisers use the same misleading metric.

Before you report a competitor, check your own claims. The same evidence standard applies to you. A review of your published attribution claims is a sensible first step.

A versioned disclosure process keeps that decision auditable from label to withdrawal.

Common questions