United Kingdom

The Enterprise Act 2002 (EA02), Part 3 Mergers. The Competition and Markets Authority (CMA) has published extensive guidance on the EA02 including Mergers: Guidance on the CMA’s jurisdiction and procedure (CMA2).

The regime is voluntary and non-suspensory; see Question 4.10 for discussion of when notifying is appropriate/advisable and Question 3.8 regarding the CMA’s ability to call-in non-notified deals.

Firms designated with Strategic Market Status under the Digital Markets, Competition and Consumer Act 2024’s digital markets regime are subject to mandatory and suspensory notification obligations where the transaction value is at least GBP 25 million; this is not discussed further.

The CMA, a non‑ministerial government department, is responsible for investigating mergers under the EA02.

Phase 1 decisions are taken by a Senior Director of Mergers of the CMA. Phase 2 decisions are made by an independent four-member CMA Inquiry Group drawn from the CMA Panel (23 individuals with relevant experience who are independent of the CMA executive). The CMA is currently consulting on replacing the panel; see Question 1.7.

The EA02 applies economy‑wide.

Certain sectors (e.g. water, media and telecommunications, energy and the NHS) have dedicated sectoral regulators who can utilise their expertise to advise the CMA on a merger’s implications, but the CMA takes the final decision.

Under the public interest regime, the UK Secretary of State for Business and Trade can take over decision-making where they consider that an above-threshold merger may raise public interest issues in relation to media plurality, the stability of the UK financial system or a public health emergency. The CMA will advise on competition issues while the Secretary of State will consider the public interest implications of the transaction which can supersede competition issues. The Secretary of State can also intervene under the special public interest regime in mergers involving government contractors and media which are below threshold. These regimes are not discussed in any further detail.

The UK’s foreign direct investment screening regime under the National Security and Investment Act 2021 (NSIA) is separate to the merger control regime and enforced by the government’s Investment Security Unit.

Following Brexit, the EU Merger Regulation no longer applies in the UK. The CMA and European Commission can now conduct parallel reviews of the same merger.

The CMA is party to or a member of various international co-operation arrangements and networks, including the:

• Five Eyes Multilateral Mutual Assistance and Co‑operation Framework between the CMA and the Australian, New Zealand, Canadian and US agencies;
• EU-UK Competition Co‑operation Agreement (signed on 25 February 2026, yet to be ratified), providing for cooperation between the CMA, European Commission and EU Member State competition authorities;
• International Competition Network; and
• OECD Competition Committee.

Within the UK, the CMA participates in the UK Competition Network, with the UK sectoral regulators, and the Digital Regulation Co‑operation Forum, consisting of the CMA, Ofcom, the Information Commissioner’s Office and the Financial Conduct Authority.

For mergers also subject to review under the NSIA, the CMA can exchange confidential information with the government.

In January 2026, the government published reform proposals including:

• introducing closed criteria lists for establishing:
  • parties’ shares of supply for the Share of Supply and Hybrid Tests; and
  • the evaluation of “material influence” or “de facto control”;
• increasing the deadline for submitting and considering remedies at Phase 1 from 10 to 20 working days from issuance of the decision; and
• abolishing the CMA’s independent panel system to be replaced by CMA Board sub-committees of executives, non-executives and independent experts.

The reforms were confirmed in May 2026 and proposed legislation is expected to follow.

The CMA has jurisdiction over a planned transaction that will result or has resulted in a “relevant merger situation”, which requires that:

• two or more “enterprises” have ceased or will cease to be distinct (i.e. brought under “common ownership or common control”);
• one of the three jurisdictional tests is satisfied (see Question 3.1, below); and
• the merger has not taken place, or it has been no more than four months since the merger closed or was made public.

“Enterprise” is a broad concept meaning the activities of a business that could be carried on for economic gain or reward (typically a combination of assets, business records, employees, contracts and/or goodwill). A collection of “bare assets” is unlikely to constitute an enterprise; but the transfer of assets or employees may be enough where they enable the economic continuity of a business.

Being brought under “common ownership or common control” arises where the purchaser acquires one of the following levels of control (or moves up to a higher level):

• Legal or de jure control where an outright controlling interest is acquired (i.e. more than 50% of the voting rights in the target).
• “De facto control” where the acquirer does not have more than 50% of the voting rights but, in practice, can control the policy and decisions of the business (e.g. because it typically casts more than half the votes at shareholder meetings).
• “Material influence” over the target’s commercial behaviour. Material influence is the lowest level of control that can constitute an enterprise being brought under common control (lower than the concept of decisive influence under the EU Merger Regulation). It is presumed at shareholdings of 25% or more, but can arise at shareholdings as low as 15%, depending on other factors such as voting rights, board representation and commercial agreements (e.g. consultancy services and loan facilities). Reforms are planned to increase legal certainty around this concept (see Question 1.7).

There is no formal requirement that a change of control must be on a lasting basis. In practice, the CMA is unlikely to investigate interim arrangements unless subsequent steps would occur after the four-month deadline for referring to Phase 2, such that it may lose jurisdiction to review the transaction (see Question 3.10).

The regime covers:

• acquisitions of shares or voting rights;
• acquisitions of assets comprising an “enterprise” (see Question 2.1); and
• contributions of existing businesses to form a joint venture (or assets which will, in combination, create an “enterprise”) (see Question 2.4).

Acquisitions of a minority stake in an enterprise may constitute a merger where material influence is acquired (see Question 2.1).

The acquisition of options or conditional rights are not considered until exercised or satisfied, as appropriate.

The formation of a joint venture will be caught where the assets being contributed to the joint venture comprise an enterprise and there is a change of control over that enterprise (e.g. a new parent takes control) and one of the jurisdictional tests is met.

A joint venture does not need to be structural. Contractual arrangements such as outsourcing contracts could constitute a relevant merger situation if assets and other elements are transferred as part of the arrangement which are sufficient to constitute an enterprise (see Question 2.1).

A sequence of transactions between the same parties within a two-year period may be treated by the CMA as having occurred simultaneously on the date on which the latest of them occurred.

A set of interrelated transactions (e.g. an asset swap) which creates more than one relevant merger situation will typically be treated as a single transaction where the elements are interconnected and part of the same overall commercial transaction.

The EA02 applies to relevant merger situations where two or more enterprises have ceased or will cease to be distinct (see Question 2.1), and the transaction meets any one of the following thresholds:

• Turnover test. The UK turnover of the enterprise being acquired exceeds GBP 100 million; or
• Share of supply test. At least one enterprise ceasing to be distinct (e.g. the party(ies) acquiring control and the target) has UK turnover exceeding GBP 10 million (the “safe harbour”), and the enterprises together supply or acquire at least 25% of goods or services of a particular description in the UK or a substantial part of it (with an increment in this share resulting from the transaction) (see Question 3.5 for information on how this is calculated and on what factors); or
• Hybrid test. One of the enterprises concerned supplies or acquires at least 33% of goods or services of any description in the UK (or a substantial part of it); the same enterprise has UK turnover exceeding GBP 350 million; and any other enterprise concerned has a UK nexus (see Question 3.6).

Note that different thresholds apply under the regimes for water and sewerage and the public interest regime (see Question 1.4). For the public interest regime, the turnover test is reduced to GBP 70 million in UK turnover, and there is no safe harbour for the share of supply test. The special public interest regime applies to below-threshold mergers.

Turnover is the consolidated, gross “ordinary course” revenue of an enterprise and all entities over which it exerts control (excluding the sellers), net of rebates, VAT and similar sales taxes through sale or supply to customers in the UK.

The relevant period is the business year preceding either the date on which enterprises ceased to be distinct (completed mergers) or the date of the CMA’s Phase 2 reference decision (proposed mergers), subject to adjustments for subsequent acquisitions or disposals.

Detailed methodology for the calculation of turnover is set out in the Enterprise Act 2002 (Merger Fees and Determination of Turnover) Order 2003 (SI 2003/1370) (as amended), with guidance, including on specific sector considerations and joint venture allocation rules, in CMA2 Appendix A.

There are no asset-based thresholds; see Question 2.1 for discussion on how assets can satisfy the definition of an enterprise.

Jurisdictional thresholds are expressed in pounds sterling.

The CMA will accept currency conversions based on the exchange rate applicable at the date of the relevant accounts (Bank of England exchange rates are usually accepted).

The share of supply and hybrid tests use a share of supply concept, which the CMA calculates by reference to “any reasonable description of a set of goods or services” in the UK or a substantial part of the UK.

The EA02 lists value, cost, quantity, capacity, users, employees, or any other criteria as bases for measuring the share of supply: this is not a formal economic market definition. The CMA has proposed reforms to introduce closed criteria; see Question 1.7. Note that the share of supply test requires an increase in the share of supply be brought about by the transaction (but no materiality threshold exists, any increase is sufficient).

The geographic frame of reference must be of such size, character and importance to merit consideration for merger control purposes, assessed by reference to size, population, social, political, economic, financial and geographic significance. In practice, a single town has been found to be sufficient.

The turnover and share of supply thresholds require UK turnover or supply/purchase of products or services in the UK or a substantial part of the UK.

The hybrid test explicitly requires that the party that does not meet the share of supply and UK turnover requirements has a “UK nexus”, meaning it supplies goods or services to UK customers, carries on activities in the UK, or is registered in the UK.

There is no exemption for foreign‑to‑foreign transactions meeting the jurisdictional tests. However, in practice, the CMA is unlikely to launch an investigation into a transaction with no link to the UK. The CMA has adopted a policy of “stepping back” on global mergers that do not have a specific impact in the UK, if remedies accepted in another jurisdiction will resolve competition concerns in the UK.

Noting the regime is voluntary, there are three exceptions to the CMA’s duty to refer a merger to Phase 2 (see Question 4.12) which play into evaluating whether to notify or submit a briefing paper (see Question 4.10):

• where the relevant market’s annual value is GBP 30 million or less;
• where the merger is not sufficiently advanced that it is likely to proceed; and
• if relevant customer benefits outweigh any competition concerns (see Question 5.2).

Yes. The CMA’s Mergers Intelligence function monitors M&A activity via press coverage, trade publications, Companies House filings and third-party complaints. It will often issue an enquiry letter to transaction parties to establish via informal questions whether it has jurisdiction to review a transaction and whether any potential competition concerns may arise before taking a decision on whether to launch a Phase 1 investigation.

The CMA can launch a Phase 1 investigation of a merger and assess jurisdiction and substance in parallel; see Question 3.8 in relation to the CMA’s separate information gathering powers. Since the CMA’s share of supply test (see Question 3.1) can be applied very flexibly, it may be used creatively to assert jurisdiction in this Phase 1 review.

The CMA must establish in its Phase 1 decision that it has jurisdiction (and that there is a realistic prospect of a substantial lessening of competition (SLC)) before it refers the merger to Phase 2 or considers undertakings in lieu of reference (UILs). The special public interest regime applies to below-threshold mergers (see Question 3.1).

The CMA has four months to launch a Phase 2 review from completion of the merger or from the earlier of when material facts were made public or given to the CMA. Limited statutory extensions exist (e.g. for failure to provide information or for remedies discussions).

Noting filing is voluntary, if the thresholds are not met, parties may consider submitting a briefing paper to the CMA to confirm that the transaction does not give rise to a relevant merger situation (see Questions 3.8 and 3.9 on call-ins, and Question 4.10 on the issue of whether to notify).

Notification is voluntary.

There is no standstill obligation.

However, the CMA has the power to impose initial enforcement orders at Phase 1 or interim orders at Phase 2 (referred to as “interim orders” collectively) to prevent pre‑emptive action in completed or anticipated mergers which might prejudice the CMA’s investigation or related actions (such as remedies).

Parties can make a detailed, reasoned request for a derogation from an interim order where necessary.

Where pre-emptive action has already occurred, the CMA can order it to be reversed.

Filing is voluntary, and there is no standstill obligation absent any interim orders (see Question 4.2).

Neither party is legally responsible for submission. In practice, the acquirer typically leads on notification. Parties will usually file jointly for joint ventures.

There is a filing fee which is determined by the UK turnover of the target. The acquirer typically pays. Fees are invoiced after the final decision, with payment due within 30 days.

Exemptions from filing fees exist for certain small and medium-sized businesses and for acquisitions of non‑controlling interests investigated on the CMA’s own initiative (provided the parties did not voluntarily submit a Merger Notice).

There is no filing fee for submitting a briefing paper (see Question 4.10) (but the fee is payable if a Merger Notice is later submitted) or in relation to special public interest cases.

Filing is voluntary.

Parties can notify once there is a good faith intention to proceed (e.g. signed heads of terms, finance in place, board-level consideration). In practice it is not possible to notify a confidential transaction as the CMA will issue a public invitation to comment.

The CMA will usually only accept a briefing paper once there is a signed agreement (see Question 4.10).

In the case of a public bid, the CMA will expect at least a public announcement of a firm intention to make an offer, or the announcement of a possible offer, in order to open a Phase 1 investigation.

Filing is voluntary, therefore, there is no deadline for submission. However, delay risks the CMA opening an own‑initiative investigation in order that it is not timed out by the four‑month deadline for commencing a Phase 2 review (see Question 3.10).

The CMA’s Merger Notice template (found at www.gov.uk/government/publications/mergers-forms-and-fee-information) sets out the required information, including contact information, transaction details and rationale, description of the parties’ businesses, revenue data, discussion of the counterfactual, market definition, market shares, discussion of the competitive assessment, efficiencies and customer benefits, and third-party details.

The parties must provide core transaction documents (e.g. sale and purchase agreement, press releases, annual reports and business plans), plus internal documents addressing the transaction rationale and competitive assessment. If the parties have a combined horizontal share of 15% or more, or a vertical/adjacent share of 30% or more, ordinary course business documents analysing competitive and market conditions in the relevant markets must also be provided. The CMA also requires a description of how these documents were identified.

There are no formalities required other than signed declarations verifying the accuracy of information in the notification and confirming the appointment of legal representatives.

Notification is voluntary. However, the CMA’s Mergers Intelligence Committee monitors for M&A activity and will often contact parties for information about non-notified deals (see Question 3.8). Parties typically submit a formal notification where they anticipate that the CMA will want to investigate the potential competitive effects of the transaction.

Instead of notifying, parties may elect to submit a briefing paper to the Mergers Intelligence Committee. Briefing papers (maximum five pages) are informal submissions that enable proactive engagement with the CMA to give some level of certainty that the transaction will not be called in for a formal review. They are commonly submitted where the parties are confident the transaction either does not qualify for review or will not give rise to substantive competition concerns.

The CMA aims to respond to briefing papers within a matter of weeks from submission, either calling the transaction in for a formal notification or confirming it has no further questions. The latter does not preclude it from opening an investigation, subject to the four-month deadline (see Question 3.10).

Pre‑notification engagement is strongly encouraged where a formal notification is made.

The CMA aims to conclude pre-notification within 40 working days from submission of a complete draft Merger Notice, ending when the CMA formally opens Phase 1.

• Phase 1. Deadline to refer to Phase 2 is 40 working days from the CMA certifying the Merger Notice as complete or possessing sufficient information in an own‑initiative case:
  • For cases raising no serious competition concerns, the CMA aims to issue clearance within 25 working days.
  • The CMA has a statutory duty to refer a transaction to Phase 2 where it finds a realistic prospect of an SLC (subject to the four-month time limit (see Question 3.10)). Where the parties offer remedies (known as undertakings in lieu of reference (UILs)), the Phase 1 timeline is extended by up to 50 working days from the SLC finding, further extendable once by 40 working days.
  • The parties may request a statutory fast‑track to Phase 2 at any time before the end of the Phase 1 review period, including during pre-notification.
• Phase 2. Deadline of 24 weeks from the Phase 2 referral decision, extendable by up to eight weeks for “special reasons” (a low bar, in practice):
  • The CMA and the parties can further agree an extension to the 24-week deadline. There is no fixed cap, and extensions may be agreed more than once.
  • If remedies are required, the Phase 2 deadline is extended by up to 12 additional weeks (further extendable by six weeks).

In Phases 1 and 2, the review periods can be stopped by non-compliance with formal requests for information.

Deadlines are calculated by reference to working days, which exclude weekends, Good Friday, Christmas Day, and public holidays.

A non-problematic deal can expect to achieve clearance within 25 working days. The total time from signing will depend on the time spent preparing the Merger Notice and the prenotification period (which the CMA aims to conclude within 40 working days; see Question 4.11) and whether these have commenced before signing. A typical timeframe would be three to five months from signing.

The briefing paper process is usually completed within a matter of three to four weeks; see Question 4.10 (plus preparation time after signing).

The CMA’s merger control process runs in parallel to the City Code on Takeovers and Mergers, which imposes strict requirements and timetables on public offers. Regulatory conditions precedent are permitted and the offer timetable will be suspended pending their fulfilment, provided they are considered material. A longstop date must be included in the offer, which can accommodate the timeframes for regulatory clearances, including Phase 2 processes.

Third parties play an important role throughout Phases 1 and 2:

• In Phase 1, the CMA will issue a public “invitation to comment” and will make direct outreach to competitors, customers and suppliers identified in the Merger Notice via questionnaires, calls, meetings or formal information requests.
• At Phase 2, third parties may respond to the CMA’s Phase 1 decision and may receive information requests. Key third parties may give evidence at oral hearings and be invited to comment on key documents through the process.
• Proposed remedies at Phases 1 and 2 are also subject to public consultation.

The CMA will usually make informal information requests to the parties. It also has statutory powers to require information from parties or third parties using a formal “Section 109 notice”, which can compel the production of documents, estimates, forecasts or other specified information and attendance as a witness. These powers can be used outside the UK (provided certain statutory connection conditions are met).

The CMA must protect specified information where disclosure would significantly harm legitimate business or private interests of both the parties and third parties, subject to statutory exceptions. Parties are able to identify confidential information in their submissions for redaction.

CMA transparency and disclosure policies guide handling and publication (e.g. the “put-back process”) to ensure confidential information is excluded from the CMA’s decisions and other published materials about the case.

The CMA applies the same substantive assessment at Phases 1 and 2: it examines whether a relevant merger situation has resulted or may be expected to result in an SLC within any market for goods or services in the UK (see Question 4.12). An SLC arises when a transaction harms rivalry between firms, to the detriment of customers.

There are no fixed thresholds based on market share or the number of remaining competitors to determine whether a loss of competition is “substantial”. The CMA assesses competitive effects by reference to “theories of harm” including horizontal unilateral and coordinated effects, vertical effects, conglomerate effects and potential competition. The SLC is assessed against the counterfactual, being the conditions of competition that would have prevailed absent the transaction.

The evidential threshold for identifying an SLC, however, differs between review phases. Phase 1 assesses whether there is a “realistic prospect” of an SLC (greater than fanciful but less than 50%). At Phase 2, the SLC is assessed on the balance of probabilities (greater than 50% chance).

Efficiencies can comprise either rivalry-enhancing efficiencies or relevant customer benefits.

Rivalry-enhancing efficiencies increase the merged firm’s incentives to act as a stronger competitor by reducing marginal costs, incentivising lower prices or better quality/service. They may operate to prevent or outweigh an SLC, if they can be shown to enhance rivalry in the relevant market(s), are timely, likely and sufficient, merger-specific, and benefit UK customers.

Relevant customer benefits are efficiencies which generate benefits for direct, indirect and future customers in the UK, other than through improved competition in the relevant market (e.g. greater innovation from combining unique assets, or reduced carbon emissions). They will not prevent an SLC finding but may outweigh it and any adverse effects arising from it. At Phase 1, the CMA does not have to launch Phase 2 where relevant customer benefits outweigh the SLC finding. At Phase 2, they may inform remedy design or a finding that detriments are outweighed.

Phase 1 and 2 procedures include a number of formal and informal mechanisms for communication between the CMA and the parties through submissions, requests for information and responses, informal meetings or calls and formal hearings and discussions on remedy proposals.

Informal engagement on remedies can commence at any time, including during pre-notification — early engagement is encouraged.

At Phase 1, parties can formally offer UILs up to five working days from the CMA’s decision, using the Phase 1 Remedies Form.

At Phase 2 and after publication of the CMA’s interim report at weeks 12–14, parties may submit formal remedy proposals using the Phase 2 Remedies Form; however, without prejudice engagement on remedies can begin from the start of Phase 2.

At Phase 1, remedies should enable a clear-cut removal of the SLC. At Phase 2, remedies offered by the parties or imposed by the CMA should remedy, mitigate or prevent the SLC. The CMA has powers to prohibit or unwind a merger if it considers that necessary to address the SLC.

The CMA has historically preferred structural remedies (e.g. divestments) to restore competition and minimise monitoring. However, it has recently signalled greater openness to behavioural remedies (e.g. licensing or interoperability commitments) where effective and proportionate.

There is no standstill obligation. However, interim orders (see Question 4.2) and the terms of remedies may prohibit closing. Remedies will often include monitoring trustee mechanisms, and the CMA can also enforce them through directions, court action, or the imposition of fines.

The CMA publishes its decisions. Redacted versions of the decision are issued to the external legal advisors of the parties before public announcement, with publication of a non-confidential version of the decision occurring following consultation with the parties.

CMA decisions take effect immediately.

Competition restrictions which are directly related and necessary to the transaction will be exempt from the Competition Act 1998 prohibition on anti-competitive agreements, but must be self-assessed by the parties.

All decisions (clearance or otherwise) are subject to judicial review. The application must be made within four weeks of notification, or publication, of the decision (whichever is earlier) before 5pm.

Notification is voluntary, therefore, there are no sanctions for late or non‑notification.

There is no standstill obligation, absent any imposed interim order (see Question 4.2). Breach of an interim order prohibiting closing or integration can attract fines of up to 5% of worldwide group turnover. Pre‑closing integration planning is permissible in principle but must avoid steps that risk pre‑emptive action or breach interim orders, noting derogations may be sought.

Knowingly or recklessly supplying false or misleading information, or intentionally altering, suppressing or destroying requested documents, are both criminal offences subject to imprisonment or fines. Sanctions have not been imposed on natural persons to date.

Civil fines can be imposed by the CMA for failure to comply with a formal notice requesting information of up to GBP 30,000 plus a daily penalty of up to GBP 15,000 per day.