How best to make a competition or consumer law complaint and what happens next
Source: gov.uk (2025-10-07)

How to report a potential breach of competition or consumer law to the Competition and Markets Authority (CMA), and what to expect from us.

The CMA welcomes complaints about:
- potential anti-competitive behaviour, such as abuse of market power or agreements that prevent or distort competition
- potential breaches of consumer law, for example misleading practices (https://www.gov.uk/government/publications/what-businesses-need-to-know-about-unfair-commercial-practices) – including providing misleading information or omitting material information – unfair contract terms (https://www.gov.uk/guidance/how-to-write-fair-contracts), or other practices that harm the interests of consumers or fair-dealing businesses
You can also report a cartel to the CMA. A cartel is when 2 or more rival businesses agree to act together instead of competing. For example, they might agree what prices they are going to charge, or divide a market so they are sheltered from competition. The process for reporting cartels (https://www.gov.uk/guidance/tell-the-cma-about-a-competition-or-market-problem#report-a-cartel-to-the-cma) is different and not covered here.

This guide outlines what a well-reasoned complaint to the CMA looks like and details the positive impact that making a well-reasoned complaint may have on the overall complaints process. It also explains what you can expect when you make a complaint to us.

Making a complaint

You can make a complaint about suspected anti-competitive behaviour or potential breaches of consumer law by:
- using the CMA’s online form (https://www.gov.uk/guidance/contact-the-cma), which will ask you for: a description of the issue, including its impact; any supporting evidence you have; and details about yourself and (where relevant) your organisation
- calling the CMA’s General Enquiries team on xx-xxxx-xxxx
- emailing xxx@xxx.xx (mailto:xxx@xxx.xx)
Before investing too much time and resources in preparing your complaint, you can outline your concern to the CMA first. We may then decide to contact you to discuss it further, including what more information or evidence could enhance your complaint.

For information about pre-complaint discussions in the context of competition law complaints, read paragraphs 3.17 to 3.20 of our guidance on the CMA’s investigation procedures in Competition Act 1998 cases (https://www.gov.uk/government/publications/guidance-on-the-cmas-investigation-procedures-in-competition-act-1998-cases) (CMA8).

Making a well-reasoned complaint

The CMA does not have a template you must use for making a complaint and you can make your complaint in the form you think best supports it.

What a well-reasoned complaint looks like may, to an extent, depend on the circumstances of the case. There may also be some differences between what a well-reasoned competition law complaint and a well-reasoned consumer law complaint looks like. But there are certain elements that you should include to help us review it more easily and quickly.

Provide as much hard evidence as you have

For both competition and consumer law issues, a well-reasoned complaint will set out the problem succinctly. It will also be supported by as many of the following as possible, and clearly backed by evidence (not conjecture):
- the nature of the potential infringement
- any evidence of the potential infringement (including any available copies of documentary evidence) and details of how and when you obtained it
- who may have, or where we may find, additional evidence
- the businesses involved, what they do, their turnover and their position in the market
- the affected products or services and the market(s) that is/are relevant to the alleged conduct
- the impact of the alleged conduct on the market(s), and the nature and extent of harm to consumers and fair-dealing businesses
- any initial views on how best to remedy the infringement and the harm caused by it
If you are reporting a potential breach of consumer law, you could also:
- explain how consumers might experience the alleged conduct – for example, you could use screenshots to show the consumer’s journey when buying a product or service
- provide evidence of how the business is breaking consumer law – for example, by providing relevant studies, customer surveys, reports or other hard evidence
Explain why you think the CMA should prioritise your complaint

A well-reasoned complaint may also address, insofar as possible, how the subject matter of the complaint aligns with our prioritisation principles (https://www.gov.uk/government/publications/cma-prioritisation-principles), including setting out:
- why the CMA is best placed to act
- why the conduct is of strategic significance for the CMA, including by taking account of the CMA’s annual plan (https://www.gov.uk/government/publications/cma-annual-plan-2025-to-2026) and the UK government’s strategic steer to the CMA (https://www.gov.uk/government/publications/strategic-steer-to-the-competition-and-markets-authority)
- the benefits that CMA intervention could have
- how an intervention would be an efficient use of CMA resources
Our commitment to complainants

What you can expect from us

You can expect us to:
- consider your complaint carefully
- acknowledge your complaint and, if there is a realistic prospect of us investigating it, keep you updated
- try to protect your identity and any confidential information you provide while we consider your complaint
We will acknowledge your complaint but may not provide a substantive response

We will acknowledge every complaint we receive. But given the volume of complaints, we cannot respond substantively to each one. If you have not heard from us – beyond an acknowledgement – within 6 weeks (as described below), then it is likely that we do not think there is a realistic prospect of us investigating your complaint.

We will keep you updated if there is a realistic prospect of us investigating

If there is a realistic prospect of us prioritising a competition or consumer law investigation into the matter you have raised, we will aim to:
- contact you within 6 weeks to ask for more information or, if appropriate, to provide an update on our consideration of the matter
- update you at regular intervals (if we are not already in contact with you) until we have either launched an investigation or decided that an investigation is not an administrative priority
How often we update you, and in what level of detail, will depend on the nature of the case, including the need to protect any potential investigation.

The CMA appreciates that if you complain about a potential breach of the law, you likely want us to intervene as soon as possible. The time we will need to consider a complaint, and potentially launch an investigation, will depend on factors, such as the:
- complexity of the matter
- completeness and quality of the information available to us
- potential work being done by others
- availability of appropriate CMA resources
We will objectively prioritise which cases to investigate

The CMA must make efficient and effective use of our resources. When deciding which matters to investigate, we take into account our prioritisation principles (https://www.gov.uk/government/publications/cma-prioritisation-principles). In summary, we consider:
- the strategic significance of the sector and/or trader
- how substantial the likely positive impact of our action would be
- whether we are best placed to act or whether there is an appropriate alternative to CMA action
- the resources required over the estimated length of the proposed case
- the types and degree of any risks associated with CMA action, including the risk to a successful outcome to any investigation
If, having engaged with you (beyond an acknowledgement) about your complaint, we decide that an investigation is not an administrative priority, then we will explain our reasons to you.

If we decide not to prioritise an investigation, we may still take informal action. For example, we may send a warning or advisory letter (https://www.gov.uk/guidance/warning-and-advisory-letters-essential-information-for-businesses) to remind a business of its legal obligations. But if we take informal action then, due to restrictions on what information we can disclose, we may not be able to tell you that we have done so.

We will respect confidentiality to the extent allowed by law

We realise that you may not want details about you or your complaint to be disclosed, either to the business you are making a complaint about, or to the wider public.

If you have specific concerns about disclosure of your identity or information you provide to us, you should tell us. You can make a complaint anonymously, although it may be harder for us to act on information provided anonymously. If you make a complaint anonymously, avoid including information that could allow your identity to be deduced.

The CMA must comply with strict rules about the disclosure of information (https://www.gov.uk/government/publications/transparency-and-disclosure-statement-of-the-cmas-policy-and-approach) it receives as well as data protection legislation (https://www.gov.uk/data-protection). We also think carefully about how to disclose complaints information, and may redact, anonymise or aggregate details to protect confidentiality.

Under Part 9 of the Enterprise Act 2002 (https://www.legislation.gov.uk/ukpga/2002/40/part/9), we are prohibited from disclosing certain confidential information (except in certain specified circumstances) and we aim to keep the identity of complainants confidential while we are considering whether to pursue a complaint.

We aim not to disclose your identity, and/or the information you have provided, unless an investigation has been opened and it is necessary to do so to allow the business under investigation to respond properly (for example, where we have made a provisional finding). We will give you an opportunity to comment before disclosing your identity or any of your information.