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UK Competition Law in Acquisitions: Merger Control

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Written by Brad Askew Solicitor (non-practising)
Brad is on the roll of solicitors of England & Wales but does not hold a practising certificate and does not provide legal advice.
Updated June 2026 · England & Wales
When one business buys another in the UK, competition law can have a significant say in whether the deal goes ahead, how it is structured, and on what conditions. The rules are designed to stop transactions that would harm competition in a market, push prices up, or squeeze out smaller rivals. For buyers and sellers, understanding the framework early on matters, because clearance issues discovered late in a deal can derail negotiations, delay completion, or lead to unwanted remedies being imposed. In this guide I walk through how UK merger control operates, which authority looks at deals, the thresholds that trigger review, and the factors that shape the outcome. It is written as general information for business owners, directors, and advisers thinking about an acquisition, merger, or sale in England, Wales, Scotland, or Northern Ireland.

What this document is

UK competition law covers the rules that keep markets working fairly, stopping businesses from abusing market power or striking deals that harm customers and competitors. A specific strand of this framework, usually called merger control, looks at transactions where two businesses come together, whether by share purchase, asset sale, joint venture, or some other structure that results in a change of control.

The central question the regulator asks is whether the combined business, after the deal, would have the ability and incentive to behave in ways that substantially reduce competition in one or more markets. The main legislation sits across the Competition Act 1998 and the Enterprise Act 2002, with the Enterprise Act providing the core merger control regime.

I am writing this as general background, not as legal advice on any specific transaction. If you are weighing up a deal, the competition analysis should sit alongside your tax, commercial, and employment due diligence rather than being treated as an afterthought.

How to use this document

  1. Map the deal and the markets involved. Before worrying about thresholds, get a clear picture of what is being bought, which products or services each side supplies, and where customers actually buy from. The relevant market is often narrower or broader than people assume, and that definition shapes every later question about competition effects.
  2. Check whether the UK merger thresholds are met. Look at the target's UK turnover and the combined share of supply the parties would have after the deal. If either of the statutory tests is met, the Competition and Markets Authority has jurisdiction to examine the transaction, even though notification in the UK is voluntary rather than mandatory.
  3. Decide whether to notify the CMA. Unlike some jurisdictions, UK merger control does not force parties to file. You can choose to notify and seek clearance, or complete without notifying and accept the risk the CMA may call the deal in. Which route is sensible depends on the competition risk profile and commercial timetable.
  4. Prepare for Phase 1 review if the CMA engages. A Phase 1 investigation typically runs to a statutory timetable once a complete submission is accepted. The CMA gathers evidence from the parties, customers, and competitors, then decides whether the deal raises a realistic prospect of a substantial lessening of competition.
  5. Address any concerns through remedies or Phase 2. If the CMA has concerns at Phase 1, parties can offer undertakings, often divestments, to resolve them. If that is not possible, the matter moves to an in-depth Phase 2 investigation, which can end in clearance, clearance with conditions, or a prohibition.

Common questions

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Common questions

Q Is it compulsory to notify the CMA of an acquisition in the UK?
No. The UK merger control regime is voluntary, which means you are not legally required to file a deal with the Competition and Markets Authority before completion. That said, the CMA has the power to investigate qualifying mergers on its own initiative, including after completion, so many parties choose to notify when there is a real chance of competition concerns being raised.
Q What are the main thresholds that give the CMA jurisdiction?
The CMA can review a transaction if the target's UK turnover exceeds a statutory figure, or if the deal creates or enhances a combined share of supply of goods or services of at least 25% in the UK or a substantial part of it. The specific turnover figure is set by legislation and has been updated over time, so check the current threshold on gov.uk before relying on it.
Q What does substantial lessening of competition actually mean?
It is the legal test the CMA applies when deciding whether a merger is problematic. In practical terms, the authority looks at whether the combined business would be able to raise prices, reduce quality, cut innovation, or weaken choice compared with the situation that would have existed without the deal. The assessment is forward-looking and evidence-based rather than purely theoretical.
Q How long does a CMA merger review take?
Phase 1 reviews follow a statutory timetable once the CMA formally starts the clock on a complete notification. If the deal moves into Phase 2 for deeper investigation, the process takes significantly longer and involves more detailed evidence gathering, hearings, and analysis. Timing can also slip if parties need to respond to information requests or negotiate remedies.
Q Can the CMA block a deal that has already completed?
Yes. Because UK merger control is voluntary, parties can complete without filing, but the CMA retains the power to investigate qualifying mergers after closing. If concerns are found, the authority can require divestments or other remedies, and in serious cases unwind the transaction. That risk is one reason many parties still notify deals with competition sensitivity.
Q Do overseas-to-overseas deals ever fall within UK jurisdiction?
They can. If a target generates sufficient UK turnover, or if the merged business would hold a meaningful share of supply in the UK, the CMA may have jurisdiction even where both parties are headquartered abroad and the deal is signed elsewhere. International transactions often need parallel competition analysis across several regulators.
Q What types of remedies does the CMA typically accept?
Structural remedies, usually the divestment of a business, brand, or set of assets to a suitable buyer, are generally preferred because they directly restore competition. Behavioural remedies, such as commitments on pricing or access, are accepted in narrower circumstances. The right package depends on the specific theory of harm the CMA has identified.
If you're dealing with this kind of situation, speak to an experienced legal adviser who can walk you through it — from £89.

Sources

This guide is based on primary UK law and official guidance.

Brad Askew, Solicitor (non-practising)

Written & reviewed by

Brad Askew Solicitor (non-practising)

Brad is on the roll of solicitors of England & Wales but does not hold a practising certificate and does not provide legal advice. LegalDocuments.co.uk is not a law firm and does not provide regulated legal advice.

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Legal disclaimer
This article is for general information only. It is a tool to help you find your way — not legal advice, and not a substitute for speaking to a qualified adviser about your situation.