How to Respond to a CMA Market Investigation in the UK (2026): Step‑by‑step Process, Timelines & Evidence Checklist

A CMA market investigation UK businesses now face has become a more probable, and more consequential, regulatory event under the Competition and Markets Authority’s 2026 enforcement agenda. A market investigation is a statutory, in‑depth examination of whether features of a market prevent, restrict or distort competition, and it carries the power to impose binding remedies on companies that have breached no law at all. For in‑house counsel, compliance teams, directors and deal teams, the practical question is no longer academic: what do you actually do in the first 24 hours, and across the following months, when your sector is referred?

This guide sets out a step‑by‑step response process, statutory timelines, an evidence checklist and the remedies and appeal routes you must plan for.

1. Overview, What is a CMA market investigation?

A market investigation is a formal process under the Enterprise Act 2002 by which the CMA examines an entire market, not a single company’s conduct, to determine whether an “adverse effect on competition” (AEC) exists. Unlike an antitrust enforcement case under the Competition Act 1998, a market investigation does not require any finding of illegal behaviour. Features of a market, high concentration, structural barriers, weak customer switching, or vertical relationships, can each justify intervention. The distinction matters: a company can be entirely compliant with competition law and still be subject to divestment or conduct remedies at the end of a market investigation.

What triggers a market investigation

There are three principal routes into a CMA market investigation UK companies should understand:

• Reference following a market study. The most common route. The CMA opens a market study, gathers evidence, and if it has a reasonable suspicion of an AEC it makes a market investigation reference to its own panel under section 131 of the Enterprise Act 2002.
• Ministerial reference. The Secretary of State may, in defined circumstances set out in the Enterprise Act 2002, refer a market to the CMA.
• Own‑initiative and sector escalation. Concerns raised through complaints, super‑complaints from designated consumer bodies, or the CMA’s own market monitoring can escalate a study into a full investigation.

Once a reference is made under section 131, the investigation is conducted by an independent inquiry group drawn from the CMA panel, which operates separately from the case teams that recommended the reference.

The CMA’s objectives and possible outcomes

The CMA’s statutory objective is to remedy, mitigate or prevent any adverse effect on competition it identifies, and any resulting detrimental effect on consumers. The possible outcomes range from a clean bill of health (no AEC found), through recommendations to government or other regulators, to the imposition of legally binding structural or behavioural remedies. The CMA may also accept undertakings in lieu of making a reference, or accept undertakings as a means of implementing remedies. Because the remedies power is broad and does not depend on wrongdoing, treating a market investigation as a compliance formality is a serious strategic error.

2. Eligibility, Are you likely to be affected?

No company can opt out of a market investigation once its sector is referred, but the risk of a reference is far from evenly distributed. Understanding the indicators helps legal and compliance teams prepare before the CMA arrives.

Typical sectors and risk indicators

The CMA tends to scrutinise markets that show a combination of structural and behavioural warning signs. Watch for:

• High or rising market concentration. A small number of firms holding large combined shares, or persistent market leadership over time.
• Barriers to entry and expansion. Regulatory, capital, network or data‑driven barriers that insulate incumbents.
• Price and margin anomalies. Prices or margins that appear high relative to costs or to comparable markets, or evidence of parallel pricing.
• Weak customer engagement. Low switching rates, complex tariffs, or information asymmetries that suppress competitive pressure.
• Evidence of consumer detriment. Complaint volumes, poor quality outcomes, or vulnerable‑consumer harm.

Sectors with repeated regulatory attention, retail banking, energy, digital platforms, pharmaceuticals, funerals, housebuilding and veterinary services among them, should treat a reference as a live contingency rather than a remote possibility.

When to seek counsel and internal escalation triggers

Do not wait for a formal notice. Escalate to senior management and external competition counsel when any of the following occurs: the CMA opens a market study touching your sector; you receive an informal information request or invitation to a hearing; a super‑complaint naming your market is published; or a competitor or trade body signals that a reference is being sought. Early engagement lets you build a document map and a response team while there is still time to do so calmly.

3. Step‑by‑step: How to respond to a CMA market investigation UK

The following seven steps map the practical response from the first hours through to appeal. Each identifies the internal and external lead, the key documents involved, and the CMA’s powers to compel. Treat the timings as planning estimates, the actual programme is driven by the reference and the scale of information the CMA requests.

Step 1 (First 24 hours): Triage and immediate actions

The moment a reference or first notice arrives, the priority is preservation and control. The general counsel should take the lead, supported by external competition counsel, legal operations and IT.

• Issue a document‑preservation hold immediately. Suspend all routine deletion, auto‑archiving and destruction schedules across email, messaging and document systems.
• Identify document and data owners. Map who controls pricing files, contracts, board records and transactional datasets.
• Notify the C‑suite and the board. A market investigation is a board‑level matter with reputational and financial exposure.
• Instruct external counsel. Engage specialist competition counsel before responding substantively to the CMA.

Step 2 (24–72 hours): Confirm scope and set up the team

With preservation in place, competition counsel should lead a rapid review of the reference or notice to establish exactly what market has been referred, what theories of harm the CMA has signalled, and what deadlines apply. Convene a core response team drawing in regulatory, finance and the relevant business heads, and agree a single communication protocol so that no employee responds to the CMA independently. Establish who is authorised to speak to the case team, and set up a privileged channel for all internal analysis.

Step 3 (Days 3–14): Information audit, privilege review and forensic hold

External counsel, supported by an eDiscovery vendor and IT, should now build a detailed data map: what data exists, where it sits, in what format, and who holds it. Run an early privilege review to identify legally privileged material and to ensure it is quarantined before any production. Confirm the forensic hold is comprehensive, including messaging platforms such as Teams and WhatsApp, and preserve metadata, because the CMA’s information‑gathering powers extend to native files and their provenance.

Step 4 (Weeks 2–6): Prepare and submit initial responses

External counsel and business subject‑matter experts prepare the first formal responses to information requests and notices to produce. Where a request is unclear, disproportionate or overlapping, engage the case team early to negotiate clarifications and, where appropriate, a phased disclosure timetable. Accurate, well‑organised early responses set the tone for the whole investigation and reduce the risk of follow‑up notices.

Step 5 (Weeks 6–12): Substantive engagement

This is the evidence‑building phase. Provide witness statements, economic and transactional data, and properly redacted documents. Engage constructively with the CMA case team, respond to its emerging thinking, and correct factual misunderstandings before they harden into provisional findings. Manage any parallel media and stakeholder communications carefully, public statements can be used as evidence and can complicate the case.

Step 6 (Pre‑remedies): Prepare for the remedies process

As the CMA moves toward provisional findings, senior counsel, economists and the board should model the remedies the CMA might propose and their commercial impact. Where sensible, prepare and offer undertakings, voluntary commitments that can resolve concerns and may avoid the most intrusive structural outcomes. Robust market‑share and effects analysis is essential here.

Step 7 (Appeals and post‑decision): Challenge and implementation

If remedies are imposed in the final report, litigation counsel and compliance should assess promptly whether to challenge the decision at the Competition Appeal Tribunal (CAT). Applications for review of market investigation decisions are made to the CAT under the Enterprise Act 2002. Appeal windows are fixed and short, so the decision cannot be deferred. Where no challenge is pursued, implement the remedies within the CMA’s timetable and build the monitoring and reporting infrastructure the remedies require.

4. Required documents and evidence checklist

The single most common failure in a market investigation is disorganised or incomplete evidence. Build your document set methodically, preserving metadata and handling privilege with discipline. Metadata should be preserved in native format wherever possible; redactions should be applied consistently and logged; and every privilege call should be recorded so it can be defended if challenged.

Core commercial and governance documents

Assemble the documents that show how the business is owned, governed and commercially structured: ownership charts, board and committee minutes, and the full suite of commercial contracts, supply, agency and distribution agreements, master services agreements, and any exclusivity or most‑favoured‑nation clauses. These establish the structural picture the CMA will test against its theories of harm.

Data and analytics

Transactional data is central to any modern market investigation. Preserve price lists, invoices, discount and rebate files, CRM records and transactional datasets in their native formats with metadata intact. The CMA and its economists will interrogate this data directly, so provenance and completeness matter as much as content.

Communications and decision records

Relevant emails, instant‑messaging logs (Teams, WhatsApp and equivalents), consultant reports and board decision records must all be captured with accurate dates. Communications frequently reveal how commercial decisions were actually made, and gaps or deletions can attract adverse inference.

5. Timeline and statutory deadlines

Timelines in a CMA market investigation UK companies encounter are partly fixed by statute and partly driven by the complexity of the market. Understanding both is essential to resource planning.

Typical CMA timeline

The lifecycle runs from reference, through an investigative phase in which the CMA gathers evidence and tests theories of harm, to the publication of provisional findings, a consultation on possible remedies, and finally a published final report. Where the CMA decides an adverse effect on competition exists, a remedies implementation phase follows the final report. In practice, businesses should plan for the investigation phase to consume many months of intensive engagement, followed by a further remedies design and implementation period.

Statutory trigger points and compliance windows

The core statutory framework sits in Part 4 of the Enterprise Act 2002. The power to make a market investigation reference is exercised under section 131, and the questions the CMA must decide, including whether any feature or combination of features of the market prevents, restricts or distorts competition, are governed by section 134. The Act sets statutory maximum periods for the investigation and for the remedies process, together with defined circumstances in which those periods may be extended. Because these outer periods are set by statute, they cannot simply be waived; missing a response deadline set by the CMA within them can expose the business to enforcement of the CMA’s information‑gathering powers.

Tactical timeline planning for businesses

Map every CMA deadline against internal capacity at the outset. Build in buffer time for privilege review and quality control before each production, resource the economic workstream early because model‑building is slow, and align board availability with the likely remedies‑consultation window. Treat the fixed statutory endpoints as anchors and work backwards from them.

6. Costs and fees

Internal costs

The largest hidden cost is diverted management and staff time. Senior executives, finance teams and business heads can lose significant capacity to the investigation, and the opportunity cost of that diversion frequently exceeds the visible legal spend.

External costs

External competition counsel, economic experts, eDiscovery providers and specialist consultants are the principal cash costs. Economic modelling in particular can be substantial in data‑heavy sectors, and document‑review costs scale directly with data volume.

Regulatory and remedy implementation costs

Where remedies are imposed, implementation can dwarf the cost of the investigation itself, structural remedies such as divestments are the most expensive, and ongoing behavioural remedies carry continuing monitoring and compliance costs.

The figures below are indicative planning ranges only; actual costs vary widely with the sector, data volumes and duration, and should be scoped with your advisers.

Remedies: structural, behavioural and undertakings

The remedies available at the end of a CMA market investigation UK businesses face fall into three broad categories. Understanding their relative cost and disruption is central to remedies strategy.

7. What changed in 2026

CMA Annual Plan enforcement priorities

The CMA’s Annual Plan signals continued, assertive use of its market investigation powers, with a stated focus on sectors where competition problems bear directly on consumers and on the cost of essential goods and services. Practitioners expect the practical effect to be more references originating from market studies, and a greater willingness to pursue robust remedies where an adverse effect on competition is found. Companies should consult the CMA’s current published Annual Plan for the priorities in force for the relevant year.

Regulatory and legislative changes to watch

The broader UK competition reform programme continues to reshape the CMA’s toolkit, including the digital markets competition regime under the Digital Markets, Competition and Consumers Act 2024 and the calibration of information‑gathering and remedies powers. Early indications suggest that businesses should expect faster‑moving processes and firmer expectations around timely, complete disclosure.

Practical implications for companies

The practical message for 2026 is preparedness. Companies in exposed sectors should have a document‑preservation protocol, a nominated response team and a shortlist of external advisers ready before any reference arrives.

8. Common pitfalls and how to avoid them

• Failing to preserve evidence or losing metadata. Issue a comprehensive preservation hold on day one and confirm that native files and metadata are preserved across every system, including messaging apps.
• Uncontrolled internal communications and off‑script statements to the CMA. Route all contact with the CMA through a single authorised channel and remind staff that internal emails and messages may be disclosable.
• Underestimating the economic analysis. Resource the economics workstream early; robust, data‑backed modelling is often decisive on both the AEC assessment and remedies.
• Missing appeal windows or statutory deadlines. Diarise every fixed deadline, and take an early view on any CAT application because the time limits are short and unforgiving.

10. Next steps

Responding effectively to a CMA market investigation UK companies now face in 2026 depends on preparation, discipline and early specialist input. Put a document‑preservation protocol and a nominated response team in place before any reference arrives, adapt the market investigation document and data request checklist above, and brief your board on the timeline, evidence obligations and remedies exposure. Where a reference is live or likely, engage experienced competition counsel at the earliest opportunity so that scope, disclosure strategy and any appeal options are managed from day one.

Sources

1. Enterprise Act 2002
2. Competition Act 1998
3. Digital Markets, Competition and Consumers Act 2024
4. CMA cases (including market studies and market investigations)
5. Competition and Markets Authority
6. Competition Appeal Tribunal (CAT)
7. The Law Society