TRW & Co · Competition, Regulatory & Investigations
Merger Control Lawyers for UK Transactions
Merger control lawyers UK acquirers instruct decide whether the Competition and Markets Authority can review a deal, how likely it is to do so and how that risk is priced. The DMCC Act raised the turnover threshold, added a hybrid test and created a small-merger safe harbour, while the CMA has reset its procedures for speed and predictability.
Key pointThe UK regime is voluntary and non-suspensory, but the CMA can investigate a completed deal within four months of it becoming public and freeze integration while it does. The real question is not whether you must file, but whether you can absorb the cost of being found after closing.
At a glance
Turnover threshold
Since 1 January 2025 the CMA has jurisdiction where the target's UK turnover exceeds £100 million, up from the previous £70 million figure.
Hybrid test added
A deal can be reviewed where one party has at least a 33% share of supply and UK turnover above £350 million, even with no overlap.
Small merger safe harbour
The share of supply route is unavailable unless at least one party has UK turnover above £10 million, removing very small deals from review.
Statutory timetable
Phase 1 runs for 40 working days after a complete notice; Phase 2 runs for 24 weeks, extendable by up to eight weeks for special reasons.
Completed deals exposed
The CMA can open an investigation within four months of completion or of material facts becoming public, and can order a completed merger unwound.
Swipe or scroll →
What UK merger control covers
Merger control is the process by which the Competition and Markets Authority (CMA) reviews acquisitions, joint ventures and minority investments that could reduce competition in the UK. The merger control lawyers UK acquirers instruct answer three questions early: does the CMA have jurisdiction, is there a realistic risk of a substantive investigation, and how should the deal documents allocate that risk?
The UK system is voluntary and non-suspensory. There is no legal obligation to notify, and parties may complete without clearance. That freedom is often misunderstood. The CMA monitors deals through its mergers intelligence function, can open an investigation on its own initiative and can impose orders that freeze integration or require a completed deal to be unwound.
The regime catches more than share purchases. A "relevant merger situation" arises when two enterprises cease to be distinct, which includes acquiring legal control, de facto control or the lower level of "material influence" over policy. Asset deals, the transfer of a customer base, contracts that pass an operating business and joint ventures can all qualify, so merger control lawyers UK deal teams rely on look at substance rather than labels.
The legal framework and the regulators
The regime sits in Part 3 of the Enterprise Act 2002. Section 23 defines the jurisdictional thresholds, section 22 governs anticipated and completed mergers referred for an in-depth review, and section 24 sets a four-month limit, running from completion or from the date material facts are made public or given to the CMA, for investigating completed deals. The Digital Markets, Competition and Consumers Act 2024 (DMCC Act) amended those thresholds with effect from 1 January 2025.
The CMA decides cases. Its guidance on jurisdiction and procedure (CMA2) explains how it applies the tests, and the CMA updated that guidance in 2025 as part of its "4Ps" programme, focused on pace, predictability, proportionality and process. Decisions are published on the CMA case pages, which are the best place to see how the authority treats a particular sector.
Review and public interest
CMA merger decisions can be challenged in the Competition Appeal Tribunal, which applies judicial review principles under section 120 rather than re-hearing the merits. Ministers retain a separate power to intervene on specified public interest grounds, such as media plurality and financial stability. National security concerns are now handled mainly under the National Security and Investment Act 2021, which runs in parallel and is covered on our foreign investment and NSIA page.
The regime applies across the whole of the UK, so Scottish and Northern Irish targets are assessed in the same way. Since Brexit, the EU Merger Regulation no longer covers UK effects, which means a large cross-border deal can face parallel reviews in London and Brussels with different timetables and outcomes.
Jurisdiction: the thresholds that matter
The first task for merger control lawyers UK investors appoint is a disciplined jurisdictional analysis. Three alternative tests now apply, together with a safe harbour for small deals.
| Test | What must be shown | Practical comment |
|---|---|---|
| Turnover test | The target's UK turnover exceeds £100 million | Calculated on the target's UK turnover, not the buyer's; the £70 million figure still applies to certain media public interest cases |
| Share of supply test | The merged parties together supply at least 25% of goods or services of a particular description in the UK or a substantial part of it, and the merger increases that share | The CMA may choose any reasonable description and metric, such as value, volume, capacity or number of workers |
| Hybrid test | One party already has a share of supply of at least 33% and UK turnover above £350 million, and another party has a UK nexus | No overlap is needed, so it can catch vertical deals and acquisitions of start-ups by established firms |
| Small merger safe harbour | The share of supply route is unavailable unless at least one party has UK turnover above £10 million | Removes very small deals from review, but turnover must be checked carefully across group companies |
Control and material influence
Jurisdiction also requires the acquisition of control. Material influence is the lowest level, and the CMA looks at voting rights, board seats, veto rights, information rights and commercial relationships. A stake that allows the holder to block special resolutions is generally treated as conferring material influence, and the CMA has found it at lower levels where other factors support it. Minority investors, including private equity and corporate venture funds, should not assume a small stake is out of scope.
The share of supply test is flexible. The CMA is not defining an economic market at this stage, and it can use a narrow description of goods or services so long as it is reasonable. That is why jurisdiction can arise in deals where the parties' combined market share looks modest on any conventional view. Our guide to UK merger control thresholds walks through worked examples.
Deciding whether to notify
Because notification is voluntary, the core judgement is whether to engage with the CMA before completion. Merger control lawyers UK boards rely on weigh the substantive risk, the CMA's likely interest and the commercial cost of delay.
- Formal notification. Suitable where there is a material overlap or a credible theory of harm. Clearance gives certainty and avoids the four-month window for a call-in after completion.
- Briefing paper. A short submission to the mergers intelligence team explaining why the deal raises no concerns. If the CMA has no further questions, parties gain comfort without a full Phase 1 review, although it is not a clearance decision.
- Proceeding without contact. Reasonable where there is no overlap, no vertical link and no realistic theory of harm. The risk is an enquiry letter after signing or completion, followed by an initial enforcement order that restricts integration.
The CMA has said it will focus on deals with distinct UK effects and is more willing to let other authorities lead on global deals where remedies elsewhere will protect UK customers. That helps, but it is a policy approach rather than a legal safe harbour.
The answer should be reflected in the transaction documents. A buyer facing real risk may want a CMA clearance condition, a long-stop date that allows for Phase 2, a "hell or high water" or remedies covenant, and a reverse break fee. Sellers want the opposite. Our M&A team negotiates these terms alongside the competition analysis.
In a voluntary regime the real decision is not whether you must file, but whether you can afford the CMA to find the deal after you have closed it.
The review process and timetable
The statutory clock does not start until the CMA confirms a merger notice is complete, so preparation matters as much as the formal phases. The CMA's targets aim to shorten pre-notification and straightforward Phase 1 cases, but they are not binding. Merger control lawyers UK clients appoint will build a realistic timetable around both.
- Jurisdiction and risk assessment. Gather UK turnover, share of supply data and internal documents, and identify overlaps, vertical links and likely complainants.
- Pre-notification. Submit a draft merger notice and respond to CMA questions. The CMA has set a target of about 40 working days for this stage, down from a historic average nearer 70.
- Phase 1. Once the notice is accepted, the CMA has 40 working days to decide whether there is a realistic prospect of a substantial lessening of competition. Simple cases may clear sooner.
- Undertakings in lieu. If the CMA finds a competition concern, the parties have five working days to offer remedies to avoid a Phase 2 reference. Statutory time limits then apply to the CMA's decision on whether to accept them.
- Phase 2. An in-depth review must normally be completed within 24 weeks of the reference, extendable by up to eight weeks for special reasons. Parties may request a fast-track reference where concerns are clear.
- Remedies and final decision. The CMA may clear the deal, accept structural or behavioural remedies, or prohibit it. For completed mergers it can order divestment.
- Review. A party may apply to the Competition Appeal Tribunal, which reviews the decision on judicial review principles within short time limits.
Interim measures
For completed or partly completed deals, the CMA routinely imposes an initial enforcement order. These orders stop integration steps such as combining sales teams, closing sites or sharing confidential information, unless the CMA grants a derogation. Breaching an order can lead to turnover-based penalties, so integration planning must be checked against the order.
How the CMA assesses competition
The test at Phase 1 is whether there is a realistic prospect that the merger will result in a substantial lessening of competition. At Phase 2 the question is whether it is more likely than not to do so. The CMA considers horizontal unilateral effects, coordinated effects, vertical foreclosure and the loss of potential or dynamic competition.
Internal documents carry great weight. Board papers, deal rationale presentations and emails describing a target as a "threat" or a way to "remove a competitor" often shape the theory of harm more than economic data. Clean, accurate drafting from the start of a process is a practical safeguard.
Brief the deal team on document discipline before the first board paper is written. Any document prepared for the transaction may be requested by the CMA, and statements written for internal enthusiasm can be read as evidence of competitive harm.
Remedies policy has moved. The CMA has signalled more openness to behavioural remedies and earlier remedies discussions, including at Phase 1, where previously it strongly preferred divestments. Parties with a clear fix should consider raising it early in pre-notification.
Documents and evidence to assemble
A complete merger notice requires substantial information. The CMA's merger notice template now asks for more information at the outset, so preparation time has increased even as review targets have shortened. Merger control lawyers UK companies use will typically ask for:
- Group structure charts and audited UK turnover for each party, with any acquisitions or disposals during the year adjusted for.
- Share of supply estimates under several reasonable product and geographic descriptions, with sources.
- Lists of top customers, suppliers and competitors, with contact details for market testing.
- Board minutes, investment committee papers, strategy documents and synergy analyses relating to the deal or the overlapping business.
- The transaction documents, including any long-form agreements, shareholder rights and ancillary commercial contracts.
- Bidding data, win/loss records and pricing analyses that show how closely the parties compete.
Where documents are held overseas or in languages other than English, allow time for collection and translation. Formal information notices under section 109 carry penalties for non-compliance, so collection should be planned, not improvised.
Common risks and mistakes
Most merger control problems arise from assumptions made before lawyers are involved. These are the issues merger control lawyers UK acquirers most often have to correct.
Treating "voluntary" as "no risk"
A non-suspensory regime lets parties complete, but the CMA can still investigate within four months of completion becoming public, impose an initial enforcement order and, if it finds a problem, require divestment. The cost of holding a business separate for months, or of selling part of it under order, can far exceed the cost of an early briefing paper or notification. The CMA's mergers intelligence team monitors press coverage, trade publications and complaints, so a deal that is publicised in the market is likely to be noticed.
Missing jurisdiction through narrow share of supply analysis
Parties often compute shares on their own preferred product description. The CMA can choose a different, narrower description and a different metric, and it is not bound by the boundaries of an economic market. A merger that looks below 25% on revenue across a broad category may exceed it on volume within a niche or within a substantial part of the UK. Analysis should test several plausible descriptions, and document the reasoning, before deciding not to engage.
Integrating too early
Once an initial enforcement order is in place, integration steps need CMA consent. Even before an order, sharing competitively sensitive information or coordinating commercial strategy before completion can raise competition law issues under the Competition Act 1998. Clean team arrangements and a clear integration plan reduce that risk. Our competition law team advises on gun-jumping and information exchange protocols.
Ignoring minority stakes and joint ventures
Investors frequently assume that a minority investment is outside merger control. Board seats, veto rights over the budget or business plan, or a dependency through supply or financing arrangements can amount to material influence. Joint ventures can also be caught where a parent contributes an existing business. These structures need the same jurisdictional analysis as a full acquisition, especially where the investor already holds stakes in competitors.
Overlooking parallel national security review
Merger control and the National Security and Investment Act 2021 are separate regimes with different tests, decision-makers and timetables. A deal can be cleared by the CMA and still require mandatory notification, and approval, under the NSIA, where completing without approval makes the deal void. Deal timetables and conditions should address both. The NSIA guide explains the mandatory sectors.
Reform: what is changing in 2026
The government published a consultation in January 2026 on further changes to the competition regime. Proposals include replacing the independent panel model for Phase 2 decisions with committees drawn from the CMA board and experts, introducing closed lists of factors for material influence and for share of supply metrics, and lengthening the Phase 1 window for considering remedies. The government has also confirmed that notification will remain voluntary.
These proposals are not yet law. Until legislation is passed, the existing tests in section 23 and the current CMA guidance apply, and deal timetables should be planned on that basis. We monitor the reform programme so that clients can adjust documentation and strategy as it develops.
Cross-border deals: EU, Bangladesh, the Gulf and Asia
Many transactions TRW & Co advises on involve parties outside the UK. The UK review is only one part of a global filing analysis, and UK jurisdiction can arise from a foreign buyer's acquisition of a business with UK sales even when neither party has a UK office.
- European Union. The EU Merger Regulation and national regimes in member states are generally mandatory and suspensory, unlike the UK. Timetables should be aligned so a UK review does not delay closing elsewhere, or the reverse.
- Bangladesh. Bangladesh's competition legislation also addresses combinations that may affect competition, and our Dhaka team advises on whether local approval is needed. Our investing in Bangladesh page covers the wider regulatory picture.
- Gulf, Singapore and China. Several Gulf states and China operate mandatory pre-closing regimes, while Singapore's regime is voluntary. Each has its own thresholds and filing requirements, so local counsel input is essential.
Coordinating filings means aligning the narrative across authorities, because regulators share information and compare submissions. Inconsistent market definitions or deal rationales across jurisdictions are a common source of difficult questions.
How TRW & Co helps
TRW & Co's London office is authorised and regulated by the Solicitors Regulation Authority. We advise buyers, sellers, investors and joint venture partners on UK merger control as part of transactional work, and we coordinate with our offices and local counsel on filings elsewhere. Where advocacy before the Competition Appeal Tribunal or in the higher courts is required, we instruct specialist counsel.
Jurisdictional analysis
We test the turnover, share of supply and hybrid thresholds, the safe harbour and the level of control acquired. The output is a clear view of whether the CMA has jurisdiction and how likely it is to engage.
Briefing papers and notifications
We prepare briefing papers, draft merger notices and responses to CMA questions. We manage pre-notification so that the formal timetable starts as early as possible.
Deal documentation
We draft conditions, long-stop dates, cooperation covenants, remedies obligations and break fees that reflect the real regulatory risk. This is done alongside our private equity and joint venture teams.
Phase 2 and remedies
We help clients respond to issues letters, develop remedies and manage hold separate obligations. Where a decision is challenged, we work with counsel on review proceedings.
Choosing merger control lawyers UK investors can rely on
Good advice is commercial as well as technical. The merger control lawyers UK investors should look for will give a clear view on jurisdiction early, explain the realistic level of CMA interest and translate that into deal terms, rather than recommending a filing by default.
We also connect merger control advice with private equity and joint venture structuring, so the competition position is reflected in the investment terms. A full list of our services is on our practices page.
Checklist for decision-makers
- Calculate the target's UK turnover and each party's UK turnover against the £100 million, £350 million and £10 million figures.
- Test share of supply under several reasonable descriptions and metrics, including any substantial part of the UK.
- Identify the level of control acquired, including veto rights and board seats in minority deals.
- Review deal documents and board papers for language that could support a theory of harm.
- Decide between notification, a briefing paper or proceeding without contact, and record the reasoning.
- Build the CMA timetable, including a possible Phase 2, into the long-stop date and conditions.
- Check whether the deal is a notifiable acquisition under the NSIA and map overseas filings.
- Plan integration so it can pause if an initial enforcement order is imposed.
To discuss a transaction, contact our London office at Holborn Gate, 330 High Holborn, London WC1V 7QH, by email at info@trw.co or by phone on +880 1779 127165.
Frequently asked questions
01Is it compulsory to notify a merger to the CMA?
No. The UK regime is voluntary, so parties can sign and complete without CMA clearance. However, if the jurisdictional thresholds are met, the CMA can investigate on its own initiative, including after completion. It can impose an initial enforcement order that stops integration and, if it finds a substantial lessening of competition, require remedies or divestment. For that reason, parties to deals with real overlaps often choose to notify formally or submit a briefing paper so that the risk is resolved before closing rather than after it.
02What are the current UK merger control thresholds?
Since 1 January 2025 there are three routes to jurisdiction. The turnover test applies where the target's UK turnover exceeds £100 million. The share of supply test applies where the parties together supply at least 25% of a description of goods or services in the UK, or a substantial part, and the deal increases that share. The hybrid test applies where one party has at least a 33% share of supply and UK turnover above £350 million and the other has a UK nexus. The share of supply routes do not apply unless at least one party has UK turnover above £10 million.
03How long does a CMA merger review take?
Pre-notification comes first and has no statutory limit, although the CMA aims to complete it in about 40 working days. Phase 1 then lasts up to 40 working days from the CMA confirming the merger notice is complete. If concerns arise and remedies are not accepted, Phase 2 must normally finish within 24 weeks of the reference, extendable by up to eight weeks. Remedy negotiations and information requests can extend the overall process, so long-stop dates should allow for the full timetable where risk is real.
04Can a minority shareholding be caught by UK merger control?
Yes. The CMA can review the acquisition of material influence, which is the lowest level of control. It considers voting rights, board representation, veto rights over strategic matters, information rights and commercial or financial links. A stake that allows the holder to block special resolutions is generally treated as conferring material influence, and lower stakes can qualify where other factors support it. Investors with interests in competing businesses should take advice before acquiring significant minority positions.
05What is a briefing paper and when should we use one?
A briefing paper is a short, informal submission to the CMA's mergers intelligence team explaining a transaction and why it does not raise competition concerns. It suits deals where jurisdiction may exist but the substantive risk is low. If the CMA has no further questions, parties gain practical comfort that it is unlikely to investigate, although a briefing paper does not produce a formal clearance decision. If the CMA does have concerns, it may ask the parties to notify formally.
06Can a CMA merger decision be challenged?
Yes. A person aggrieved by a CMA merger decision can apply to the Competition Appeal Tribunal for review. The Tribunal applies judicial review principles, so it examines whether the decision was lawful, rational and procedurally fair rather than re-deciding the competition question. Time limits are short, so the decision to challenge must be taken quickly. The government's 2026 consultation has raised wider questions about review standards, but no change has yet been made.
07Does the NSIA replace merger control for sensitive deals?
No. The National Security and Investment Act 2021 runs alongside merger control and has different triggers, a different decision-maker and a mandatory, suspensory regime for 17 sensitive sectors. A deal may need CMA engagement, an NSIA notification or both. Completing a notifiable acquisition under the NSIA without approval makes it void and can lead to civil and criminal penalties, so both regimes should be mapped at the start of a transaction.
Sources and official materials
- Enterprise Act 2002 — Part 3 merger control, including section 23 thresholds
- Digital Markets, Competition and Consumers Act 2024 — Amended thresholds and merger procedures from 1 January 2025
- CMA guidance on jurisdiction and procedure (CMA2) — How the CMA applies the tests and runs reviews
- CMA case pages — Published merger decisions and ongoing cases
- Competition Appeal Tribunal — Review of CMA merger decisions
- National Security and Investment Act guidance — Parallel mandatory regime for sensitive sectors
General information only, current as at 21 October 2026. It is not legal advice and does not create a solicitor–client relationship. It reflects the law of England and Wales unless stated otherwise; Scotland and Northern Ireland have separate legal systems, and the law changes frequently. Check current official sources and take advice on the facts of your matter.