How to Report Anti-competitive Behaviour in the UK (2026): Who to Tell, What to Include, Evidence Checklist

Knowing how to report anti-competitive behaviour can be the difference between a complaint that triggers a full investigation and one that sits unread in a regulator’s queue. The Competition and Markets Authority (CMA) has sharpened its enforcement priorities for 2026, placing digital markets, technology-transfer arrangements and cross-border cartels at the centre of its strategy. Simultaneously, post-Brexit cooperation agreements between the UK and the EU are maturing, enabling faster evidence sharing on cases with effects in both jurisdictions. This guide gives in-house counsel, compliance teams and SMEs a practical, step-by-step playbook, covering who to contact, what to include in a complaint, how to preserve evidence, and what outcomes to expect under the current UK competition law reform landscape.

1. Who to Report Anti-Competitive Activity To, CMA vs Sector Regulator

Before you file a single document, you need to direct your complaint to the right body. Sending a detailed submission to the wrong regulator wastes weeks and risks evidence degradation. In the UK, the primary route is the CMA, but several sector regulators hold concurrent competition powers and may be better placed to act in their respective industries.

When to Report to the CMA

The CMA is the appropriate body when the suspected conduct is national or multi-sector in scope and involves serious anti-competitive practices such as price fixing, market sharing, bid-rigging or abuse of a dominant position. If the conduct does not fall neatly within a single regulated sector, or if its effects cut across multiple markets, the CMA should be your first port of call. You can report anti-competitive activity directly via the GOV.UK reporting page or by contacting the CMA’s general enquiries function.

When to Report to a Sector Regulator

If the alleged conduct is confined to a regulated sector, the relevant sector regulator may investigate under its concurrent competition powers:

• Energy. Ofgem handles competition complaints in gas and electricity markets.
• Telecommunications and broadcasting. Ofcom addresses competition issues in telecoms, postal services and media.
• Rail. The Office of Rail and Road (ORR) investigates suspected competition issues in the rail sector.
• Water. Ofwat enforces competition law in the water and sewerage sector in England and Wales.
• Financial services. The Payment Systems Regulator (PSR) and the Financial Conduct Authority (FCA) have concurrent powers in payment systems and certain financial markets respectively.

Where there is doubt, reporting to both the CMA and the relevant sector regulator is permissible, the regulators operate a case-allocation mechanism to avoid duplication.

2. How to File an Anti-Competitive Complaint, Step by Step

Filing an effective complaint to the CMA or a sector regulator follows a clear sequence. Rushing the process or omitting critical information weakens the submission. Industry observers expect that, under the CMA’s 2026 enforcement priorities, well-evidenced and clearly structured complaints receive significantly faster screening decisions.

Step-by-Step Complaint Process

1. Conduct an internal preliminary review. Before contacting any regulator, verify that the conduct you have observed is genuinely likely to breach competition law (Chapter I or Chapter II prohibitions of the Competition Act 1998, or Articles 101/102 TFEU where retained). Gather initial evidence and consult legal counsel if the matter involves potential cartel activity, early legal advice protects privilege and is essential for leniency applications.
2. Identify the correct reporting channel. Use the decision flow in Section 1 above. For the CMA, the primary route is the GOV.UK anti-competitive activity reporting page. You may also contact CMA general enquiries by email or post.
3. Prepare your complaint submission. Draft a cover letter or email that sets out the essential facts clearly and concisely. Use the template fields below. Attach supporting evidence as indexed appendices.
4. Submit and retain proof of submission. Send via the GOV.UK online form or email. If using email, request a delivery receipt. Save a timestamped copy of everything you submit.
5. Follow up. If you receive no acknowledgement within 10 working days, follow up by email or telephone.

Sample Complaint Email Template

The following template can be adapted for a complaint to the CMA. Use a clear subject line such as: “Report of suspected anti-competitive conduct, [market/sector], [your reference]”.

• Your details. Full name, organisation, role, contact information, and whether you wish to claim confidentiality or anonymity.
• Parties involved. Names and addresses of the businesses or individuals engaged in the suspected conduct.
• Market description. The product or service market and the geographic scope affected.
• Description of conduct. A clear, chronological summary of the anti-competitive behaviour observed, include dates, locations, meeting details and any relevant communications.
• Evidence attached. An indexed list of supporting documents (emails, invoices, contracts, screenshots, recordings where lawful).
• Impact. Explain how the conduct harms competition, consumers or other businesses.
• Anonymity or confidentiality request. State clearly if you wish the CMA to keep your identity confidential.

Whistleblowers and anonymous reporters should note that the CMA accepts anonymous reports, but its ability to investigate may be reduced without a named contact for follow-up questions.

3. What to Include in Your Complaint, Required Fields and Priority Evidence

Understanding how to report anti-competitive behaviour effectively means knowing not just where to send your complaint, but precisely what to include in it. A complaint missing key details will be deprioritised. The following checklist ranks information by importance, from essential to desirable.

Minimum Complaint Checklist

• Identity of the complainant. Even if requesting confidentiality, provide your full contact details to the regulator. Anonymous submissions are possible but carry less weight.
• Identity of the alleged infringers. Legal names, trading names, registered addresses and, where known, the names of individuals involved.
• Market definition. The relevant product or service market and the geographic scope (local, national, UK-wide, cross-border).
• Nature of the conduct. Specify the type of infringement: price fixing, market sharing, bid-rigging, information exchange, resale price maintenance, abuse of dominance (predatory pricing, tying, refusal to supply), or other restrictive practice.
• Chronology of events. Dates of meetings, communications, tenders, price changes or market exits that evidence the conduct.
• Documentary evidence. Attach original documents wherever possible, emails, text messages, WhatsApp or Signal screenshots, contracts, invoices, tender documents, minutes of meetings, and internal memos.
• Transaction records. Pricing data, purchase orders, sales records and margin analyses that demonstrate the effect of the conduct.
• Witness information. Names of individuals who can corroborate the conduct, including their roles and contact details.
• Impact statement. Quantify, where possible, the financial harm to your business or the broader market, lost revenue, inflated input costs, or foreclosed market access.
• Previous complaints or related proceedings. Note any earlier complaints to other regulators, ongoing litigation, or related regulatory proceedings.

The CMA’s guidance, published as CMA19: Quick Guide to Complying with Competition Law, provides a useful reference for understanding which categories of conduct are most serious from a competition law reporting standpoint. Anti-competitive practices examples, such as price fixing among competitors in procurement, bid-rigging in public contracts, or an incumbent firm leveraging dominance to exclude new entrants, should be described with as much factual precision as possible.

4. Evidence: How to Gather, Preserve and Produce It

Evidence quality is the single most important factor in whether a complaint progresses to investigation. The CMA complaint process depends heavily on the documentary record available at the time of submission, and once evidence is lost, deleted or overwritten, it cannot be recreated. This section provides a practical preservation plan for compliance teams and IT departments.

Quick Preservation Checklist (for IT Teams)

1. Issue an internal legal hold immediately. Circulate a written retention notice to all relevant custodians instructing them to preserve all documents, electronic files, emails and communications related to the suspected conduct. Sample wording: “You are directed to preserve all documents, data and communications, in any format, relating to [describe subject matter] from [earliest relevant date] to the present. Do not delete, modify, overwrite or destroy any such material. This obligation applies to email, instant messages, files on shared drives, local hard drives, mobile devices, cloud storage and paper records.”
2. Isolate relevant servers and workstations. Prevent automatic overwriting of backup tapes, server logs and email archives. Disable auto-delete policies on relevant mailboxes and shared drives.
3. Export emails with full headers. Preserve messages in their native format (e.g., .pst, .eml or .mbox). Headers contain metadata, sender IP addresses, timestamps and routing data, that authenticate communications.
4. Preserve server and application logs. Export web server access logs, CRM audit trails, ERP transaction logs and any database query logs that record pricing, ordering or customer allocation activities.
5. Take forensic images where warranted. For high-value evidence, create bit-for-bit forensic images of hard drives and mobile devices using write-blocking tools. Document the chain of custody, who created the image, when, using what tool, and where the image is stored.
6. Retain metadata. Do not open, print-to-PDF or re-save original files. Each interaction can alter metadata (modification dates, author fields). Work from copies and keep originals untouched.
7. Document everything. Maintain a log of all preservation actions: what was preserved, when, by whom, and where it is stored. This chain-of-custody record is essential if the evidence is later used in CMA proceedings or private litigation.

Evidence to Prioritise If You Have Limited Resources

Where time or budget is constrained, focus on the evidence categories that carry the most weight in competition law reporting:

• Direct communications between competitors. Emails, messages or meeting notes evidencing agreements on price, market allocation or bid coordination.
• Pricing and tender documents. Internal pricing analyses, tender submissions and correspondence with customers showing coordinated price changes or suspicious bid patterns.
• Internal strategy documents. Board papers, minutes or memos referencing competitors’ behaviour, planned pricing actions or market-sharing arrangements.

Under 2026 changes to the technology-transfer regime, the CMA has increased its focus on intellectual property and cross-border licensing arrangements. If your complaint involves alleged anti-competitive technology-transfer agreements, such as restrictive licensing terms, territorial restrictions or no-challenge clauses, the likely practical effect will be that the CMA expects complainants to produce licence agreements, royalty schedules, and evidence of how the restrictions foreclose competition in relevant UK markets.

5. Confidentiality, Leniency and Whistleblowing, Risks and Protections

Deciding to report anti-competitive activity raises legitimate concerns about confidentiality and retaliation. UK law provides several protections, but they require proactive steps.

• Confidentiality requests. You may ask the CMA to keep your identity confidential. The CMA will generally respect such requests, though in certain circumstances disclosure may be required, for example, if a case proceeds to the Competition Appeal Tribunal and the respondent challenges the evidence.
• Leniency and immunity (cartel cases). If your business has participated in a cartel and wishes to self-report, the CMA operates a leniency programme. The first undertaking to report and provide comprehensive evidence may receive full immunity from financial penalties. Subsequent applicants may receive reductions. Applying for a leniency marker, a provisional place in the queue, is time-critical and should be managed by experienced competition counsel.
• Whistleblower protections. Individuals who report anti-competitive behaviour may be protected under the Public Interest Disclosure Act 1998, which shields qualifying disclosures from retaliation by employers. Workers making protected disclosures to prescribed regulators (including the CMA) have a right not to be subjected to detriment or unfair dismissal.
• Anonymity. The CMA accepts anonymous reports but recommends that reporters provide contact details under a confidentiality request instead, as this allows investigators to ask follow-up questions and significantly increases the chance of the complaint being actioned.

6. The CMA Complaint Process: From Receipt to Investigation

Understanding what happens after you file a complaint to the CMA helps set realistic expectations and enables compliance teams to prepare for follow-up requests. The process has several stages, and the CMA’s 2026 strategy affects how complaints are prioritised.

What Triggers a CMA Investigation?

The CMA is more likely to open a formal investigation when it finds credible evidence of conduct that causes material harm to competition and consumers. Key triggers include strong documentary evidence of a cartel (direct communications between competitors agreeing on prices or allocating markets), evidence of abuse of dominance in a concentrated market, and systemic harm affecting a large number of consumers or businesses. Under the CMA’s 2026 enforcement priorities, industry observers expect complaints involving digital markets and technology platforms to receive faster screening, given the authority’s stated focus on technology-driven competition harms.

7. Outcomes and Remedies, What Businesses Can Expect

The range of possible outcomes from a CMA investigation is broad. The practical consequences for both the complainant and the infringing parties can be significant.

Penalties and Typical Remedies

• No further action. The CMA may close a case if evidence is insufficient or the conduct does not meet the threshold for intervention. Complainants receive a closure letter.
• Informal resolution. The CMA may secure voluntary commitments from the businesses involved, for example, agreeing to change pricing practices or terminate restrictive agreements.
• Market study or investigation. Where the CMA identifies broader competition concerns, it may launch a market study (with the power to refer the market for a full investigation) rather than pursuing individual firms.
• Financial penalties. For infringements of the Chapter I or Chapter II prohibitions, the CMA may impose fines of up to 10% of worldwide turnover. Cartel conduct attracts the most severe penalties.
• Directions and injunctions. The CMA may direct businesses to cease the infringing conduct and may seek injunctions to prevent continued harm.
• Criminal prosecution (cartels). Individuals who participate in cartel conduct (price fixing, market sharing, bid-rigging) may face criminal prosecution under the Enterprise Act 2002, with potential custodial sentences.
• Private damages actions. Businesses harmed by anti-competitive conduct can bring private damages claims before the Competition Appeal Tribunal or the High Court. A CMA infringement decision provides a strong evidential basis for follow-on claims.
• Director disqualification. The CMA may seek competition disqualification orders against directors of companies involved in breaches of competition law.

For complainants, the practical next step after a favourable CMA decision is to assess whether a private damages claim is commercially viable. Comparative enforcement approaches, such as those seen in India’s evolving competition law framework or CCI merger control reforms, illustrate how enforcement outcomes differ by jurisdiction, an important consideration for businesses operating across borders.

8. Sector and Cross-Border Special Considerations

Competition law reporting becomes more complex when the alleged conduct spans regulated sectors or crosses national borders.

In regulated sectors such as energy, telecoms and rail, sector regulators hold concurrent powers to enforce competition law. The CMA and sector regulators operate under the Concurrency Regulations, which set out procedures for deciding which authority leads a given case. If you report to the CMA and the matter falls within a sector regulator’s expertise, the CMA will typically consult and, if appropriate, transfer the case. Reporting to the ORR for suspected anti-competitive activity in rail, or to Ofgem in energy markets, can accelerate the process where sector-specific knowledge is needed from the outset.

For cross-border conduct, such as international cartels affecting UK supply chains, the CMA has the power to investigate conduct that has an effect on competition within the UK, even if the agreement or conduct originates abroad. Under the UK/EU cooperation arrangements concluded between 2024 and 2026, the CMA and the European Commission have established practical mechanisms for sharing evidence, coordinating dawn raids and aligning timetables on parallel investigations. Early indications suggest these arrangements are materially reducing duplication and improving the speed of cross-border enforcement.

Tech-Transfer Regime 2026, Key Evidence Expectations

The 2026 changes to the UK’s technology-transfer block exemption regime have raised the bar for evidence in complaints involving IP licensing. If you are reporting restrictive technology-transfer agreements, be prepared to provide complete licence agreements, correspondence on royalty or fee negotiations, evidence of territorial restrictions and any no-challenge clauses. The CMA expects complainants to clearly demonstrate how the restrictions in question foreclose competition in the relevant UK market.

9. Quick Decision Flow and Downloadable Checklist

Use the following decision flow to determine your reporting route:

1. Is the conduct confined to a single regulated sector? If yes → report to the relevant sector regulator (Ofgem, Ofcom, ORR, Ofwat, PSR, FCA). If no → proceed to step 2.
2. Does the conduct have effects in the UK? If yes → report to the CMA via the GOV.UK reporting page. If the conduct also affects EU markets → consider a parallel report to the European Commission.
3. Is the conduct a cartel (price fixing, bid-rigging, market sharing)? If yes, and your business is involved → seek immediate legal advice on leniency before reporting. If you are a victim → file a complaint to the CMA with strong documentary evidence and preserve all materials for a potential follow-on damages claim.

A downloadable complaint template and evidence checklist covering all the fields and preservation steps in this guide is available in PDF format. The checklist mirrors the structure of Sections 3 and 4 above and can be adapted for internal compliance workflows.

Conclusion

Effective competition law reporting follows a clear sequence: identify the right regulator, structure your complaint around the fields the CMA expects, preserve evidence rigorously from day one, and understand the realistic timeline and range of outcomes. The CMA’s 2026 enforcement priorities, with their emphasis on digital markets, cross-border cooperation and technology-transfer arrangements, mean that well-prepared complaints in these areas are more likely to receive rapid attention. Use the complaint template and preservation checklist in this guide to build a submission that meets the threshold for investigation, and consult a qualified competition law specialist to protect your position throughout the process.

Sources

1. GOV.UK, Avoid and report anti-competitive activity
2. GOV.UK, Report anti-competitive activity
3. CMA, Quick Guide to Complying with Competition Law (CMA19)
4. European Commission / Your Europe, Reporting anti-competitive behaviour
5. Office of Rail and Road, Report a suspected competition issue
6. Competition and Consumer Protection Commission (Ireland), Make a competition complaint