What UK Merger Control Reform Means for Mergers, Practical Steps for Deal Teams

The UK government’s January 2026 consultation, Refining our competition regime, has placed UK merger control reform squarely at the centre of every live transaction and deal pipeline. For in-house counsel, private equity sponsors and M&A advisers, the proposals signal compressed CMA timelines, tighter governance scrutiny of panel decisions, and a renewed focus on Phase II efficiency, all of which directly affect deal certainty and timetable risk. This guide translates the consultation proposals and the CMA’s own strategic signals into a concrete, step-by-step playbook: comparison tables showing what is changing and what stays the same, a practical merger notification checklist, filing strategies that reduce avoidable friction, and deal-structuring techniques designed for mid-market and PE transactions.

Whether a transaction is already under way or still in pipeline planning, the actions outlined below can be started now, well before any legislative changes take effect. The goal is to help deal teams move from policy headlines to operational readiness.

What the 2026 UK Merger Control Reform Proposals Would Change, Summary and Practical Consequences

The Refining our competition regime consultation, published by the Department for Business and Trade in January 2026 with a response deadline of 31 March 2026, sets out proposals grouped around four themes. Each carries distinct implications for deal teams navigating merger control in the UK.

• Faster CMA decision-making. The consultation proposes streamlining Phase I timetables and accelerating the initial screening of mergers. The likely practical effect will be shorter windows for parties to submit evidence and respond to information requests, compressing the preparatory burden onto the pre-filing period.
• CMA governance and accountability. Proposals aim to strengthen the CMA Board’s oversight of merger and market-investigation decisions, introduce clearer accountability for panel chairs, and improve transparency in the decision-making process. Industry observers expect this to produce more predictable but potentially more rigorous Phase II reviews.
• Streamlining market investigations. Measures targeting the market-investigation reference process, including shortened statutory timescales and more focused remedies, would indirectly affect mergers by enabling the CMA to reallocate enforcement resources toward active deal reviews.
• Phase II procedural efficiency. While the consultation stops short of mandating wholesale changes to referral thresholds, it signals a clear direction of travel: earlier engagement on remedies, tighter control of hearing schedules, and reduced scope for procedural delays during Phase II.

For deal teams, the immediate consequence is that preparation must start earlier. Waiting until after signing to assemble the CMA evidence pack, a common mid-market practice, will become significantly riskier under compressed timelines. The competition regime changes also mean that experienced CMA practitioners will need to be involved during due diligence, not just at the filing stage.

What Stays the Same

The Enterprise Act 2002 remains the statutory backbone of UK merger control. As of 12 May 2026, the regime is still voluntary and non-suspensory: there is no legal obligation to notify a qualifying merger, and parties may close a transaction without CMA clearance. The CMA retains the power to call in completed mergers for review, creating risk for transactions that complete without notification. The jurisdictional tests, the turnover test and the share-of-supply test, are unchanged by the consultation.

What Is Likely to Require Primary Legislation vs. CMA Guidance Updates

Many of the proposed competition regime changes can be implemented through revised CMA guidance and procedural rules, for example, tightened internal timetables, earlier remedies discussions, and revised information-request protocols. However, changes to statutory time limits for Phase II investigations, modifications to the CMA Board’s legal powers, and any future shift toward a mandatory notification regime would require primary legislation through Parliament. Deal teams should monitor the government’s response to the consultation and any subsequent Competition Bill for clarity on which changes require legislation.

Merger Control UK, Voluntary, Non-Suspensory Basics That Remain in Place

Before examining how reforms will affect mergers, deal teams benefit from a concise refresh of the existing framework against which all changes are being proposed.

The CMA has jurisdiction to review a merger where either: (a) the target’s UK turnover exceeds £70 million (the turnover test); or (b) the merged entity will supply or acquire at least 25% of goods or services of a particular description in the UK, or a substantial part of it, and the merger results in an increment to that share (the share-of-supply test). The share-of-supply test is applied pragmatically by the CMA and gives it wide discretion to assert jurisdiction even over transactions that fall below turnover thresholds.

Separately, the National Security and Investment Act 2021 (NSI Act) imposes a mandatory notification regime for acquisitions of entities or assets in 17 sensitive sectors. The NSI Act operates alongside, not as a replacement for, merger control under the Enterprise Act. A transaction can therefore require NSI notification while also being reviewable by the CMA on competition grounds, and deal teams must plan for both workstreams in parallel.

Because the UK regime is voluntary, the critical decision for every deal is whether to notify pre-completion or to take the risk that the CMA will not intervene post-completion. The consultation does not propose removing voluntariness, but early indications suggest that any future shift toward a mandatory filing system would be considered in a separate legislative process.

CMA Merger Timeline, Current Practical Timetable vs. Likely Changes

Understanding the existing CMA merger timeline is essential before assessing how the reforms will affect mergers. The table below summarises the main procedural stages and typical durations based on CMA merger guidance, alongside the likely direction of travel.

For deal teams, the practical takeaway is clear: build additional buffer into transaction timetables now. If Phase I response windows compress from the current informal norm of 5–7 working days to 3–5 days, the evidence pack must be substantially complete before filing. Early indications suggest that deal teams who treat pre-notification as the primary evidence-gathering phase, rather than a formality, will gain a meaningful advantage under the reformed CMA merger timeline.

Practical Steps for Deal Teams, Pre-Signing to Post-Close Checklist

This is the operational core of the guide. Each phase below maps to a specific transaction stage and identifies the actions most likely to reduce CMA risk and protect deal certainty in light of the UK competition law reform proposals.

Pre-Deal and Due Diligence

• Action: Run a competition market screen early. Before entering exclusivity, commission a preliminary market-share analysis covering all plausible market definitions. Identify overlaps, vertical relationships, and any share-of-supply position above 25%.
• Action: Map the relevant markets. Use publicly available CMA decisional practice and industry data to define the competitive landscape. The CMA applies a pragmatic share-of-supply test, prepare for broad and narrow market definitions.
• Action: Audit internal documents. The CMA places significant weight on internal strategy documents, board minutes, and market analyses. Conduct a privilege review and identify documents that could indicate competitive harm or market power.
• Action: Assess NSI Act exposure. If the target operates in any of the 17 notifiable sectors under the National Security and Investment Act 2021, a mandatory NSI notification must be planned in parallel with any CMA strategy.
• Action: Engage competition counsel during diligence. Under compressed timelines, waiting until after signing to involve a CMA specialist creates avoidable risk. Counsel should review the evidence pack, advise on notification strategy, and identify potential Phase II risks before the SPA is agreed.

Signing and Interim Measures

• Action: Include CMA-aware conditionality in the SPA. Where voluntary notification is planned, the SPA should include a CMA clearance condition precedent with a realistic long-stop date that accounts for potential Phase II referral.
• Action: Plan for interim enforcement orders. The CMA routinely imposes initial enforcement orders (IEOs) on completed mergers and may impose interim orders during Phase I. Deal documentation should anticipate hold-separate obligations and ring-fencing requirements.
• Action: Limit integration planning communications. Pre-completion integration planning, especially exchanges of commercially sensitive information, creates enforcement risk. Implement clean-team protocols from signing.

Pre-Closing and Filing Preparation

• Action: Prepare the merger notification checklist. Assemble the CMA’s required information, party details, transaction rationale, market definitions, share data, customer and competitor lists, and internal documents, before initiating pre-notification discussions.
• Action: Draft the CMA submission to CMA standards. Front-load the submission with a clear executive summary, concise market definition, and transparent competitive-effects analysis. Avoid advocacy-heavy language; the CMA responds better to data-driven, balanced submissions.
• Action: Coordinate multi-jurisdictional filings. If the transaction also triggers review in the EU, US, or other jurisdictions, align timing and messaging across regulators. Inconsistencies between filings create investigative triggers.

Post-Closing and CMA Engagement

• Action: Monitor for CMA call-in. Where a merger has completed without notification, the CMA can open an own-initiative investigation within four months of the merger being made public or being brought to its attention. Monitor CMA merger intelligence notices and press coverage.
• Action: Comply rigorously with any IEO or undertakings. Breaching an initial enforcement order is a serious offence. Appoint a compliance officer and establish a reporting protocol from day one of any CMA-imposed obligation.
• Action: Engage constructively on remedies from the outset. Under the anticipated reforms, the CMA is expected to push for earlier remedies discussions. Deal teams that arrive at Phase II with a credible remedies proposal will negotiate from a stronger position.

Merger Notification Decision, When to Consider Voluntary Notification

Because the UK regime remains voluntary, every qualifying merger requires a deliberate notify-or-not decision. The following decision framework helps deal teams evaluate the risk systematically.

• Combined share of supply exceeds 25%. This is the threshold jurisdictional test and is also a strong substantive indicator. Mergers creating or enhancing a market position above 25% warrant serious consideration of voluntary notification.
• Unilateral effects risk. Will the merger remove a significant competitive constraint? Look at closeness of competition, evidence from bidding data or win/loss analyses, and customer switching patterns.
• Vertical or conglomerate concerns. Input foreclosure, customer foreclosure, and bundling theories of harm attract increasing CMA attention, especially in technology and regulated sectors.
• Digital platform indicators. Acquisitions by large digital platforms, even of small targets, receive heightened scrutiny. The CMA’s decisional practice in technology markets makes non-notification a high-risk strategy for platform acquirers.
• Coordinated effects. Mergers that reduce the number of significant players in concentrated markets raise tacit-coordination concerns. Transparent pricing, homogeneous products, and high barriers to entry are red flags.
• Political and regulatory sensitivity. Transactions involving essential services, media plurality, or national-security-adjacent sectors face elevated intervention risk regardless of market-share arithmetic.
• Failing-firm counterfactual. If the target is genuinely failing and there is no less anti-competitive purchaser, a failing-firm argument may support clearance, but must be evidenced rigorously with financial data, marketing evidence, and proof that exit is inevitable.

Worked Examples

Example 1, mid-market industrial deal. A private equity sponsor acquires a UK-based manufacturer of specialist valves. The combined entity will hold approximately 30% of UK supply. There are three credible competitors, and customers confirm switching is straightforward. The deal team runs a market screen during diligence, prepares the evidence pack pre-signing, and files a voluntary notification alongside a briefing note demonstrating low unilateral-effects risk. Phase I clearance is obtained within the 40-working-day window with no remedies required.

Example 2, digital platform acquisition. A global digital marketplace acquires a UK-based data-analytics start-up. The start-up’s UK turnover is below £70 million, but the share-of-supply test is met on a narrow market definition. The CMA has publicly signalled interest in platform-adjacent acquisitions. The deal team assesses that the risk of a post-completion call-in is high, and that an IEO imposed after integration would be commercially destructive. The recommended course is voluntary pre-notification with a carefully scoped market definition and a proactive competitive-effects analysis.

As of 12 May 2026, the consultation does not propose converting the voluntary system into a mandatory one. However, deal teams should monitor the government’s response and any future Competition Bill, because legislative change remains a realistic medium-term possibility. In the interim, the practical triggers for notification remain unchanged, but the consequences of getting the decision wrong are amplified by compressed review timelines and earlier CMA remedies engagement.

Filing Strategies, Evidence and the CMA Merger Timeline in Practice

A well-prepared CMA submission reduces Phase I duration and dramatically lowers the risk of a Phase II referral driven by information gaps rather than genuine competitive concerns. The following strategies reflect current best practice and anticipate the procedural tightening signalled by the uk competition law reform consultation.

• Front-load the submission. Open with a one-page executive summary that states the transaction, the parties, the relevant markets, and the competitive assessment conclusion. CMA case teams allocate resource based on initial impressions, a clear, well-structured submission signals a straightforward case.
• Prioritise evidence the CMA values. Customer data (switching analysis, win/loss records), internal strategy documents, and third-party market reports carry the most weight. Avoid burying key evidence in appendices.
• Manage multi-jurisdictional concurrency. Where the deal also triggers EU or US review, coordinate filing timelines and ensure consistent market definitions across jurisdictions. The CMA regularly contacts foreign regulators during Phase I.
• Handle confidentiality proactively. Submit confidentiality rings and redaction schedules alongside the initial filing. Delayed confidentiality claims cause procedural holdups that consume scarce Phase I days.

Fast-Track Options and Early Remedies Conversations

For mergers where competitive concerns are limited to a discrete overlap, the CMA may accept undertakings in lieu of a Phase II reference (UILs). Deal teams that identify the divestiture package early, ideally before Phase I begins, can negotiate UILs during Phase I and avoid Phase II entirely. Under the reformed regime, early indications suggest the CMA will favour this approach more actively, making pre-notification remedies planning a competitive advantage rather than an optional extra.

Phase II Merger Review, Risks, Remedies and Negotiation Playbook

A Phase II referral extends the transaction timetable by up to 24 weeks, potentially longer with extensions, and introduces a materially different investigative process led by an independent CMA inquiry group. Understanding when Phase II risk is elevated, and how to manage it, is critical in the context of the 2026 competition regime changes.

Which deals face higher Phase II risk? Industry observers expect the following categories of transactions to attract increased Phase II scrutiny in the post-reform environment:

• Digital platform and technology acquisitions, particularly where the acquirer holds a significant ecosystem position and the target provides complementary data or services.
• Mergers in concentrated regulated sectors, energy, water, telecoms, and healthcare, where the CMA applies sector-specific analytical frameworks.
• Transactions creating or strengthening a position above 33% share of supply, the CMA’s decisional practice shows that above this level, the evidential burden on parties increases substantially.
• Deals with evidence of coordinated effects risk, transparent pricing, a small number of symmetric competitors, and high barriers to entry all raise the probability of a Phase II reference.

Remedies negotiation tactics. The CMA has a strong institutional preference for structural remedies (divestiture) over behavioural remedies (undertakings to behave in a particular way). Deal teams should therefore:

• Identify a credible divestiture package early and test its viability with potential purchasers before or during Phase I.
• Prepare hold-separate and escrow arrangements to preserve the divested business’s competitive viability during the investigation period.
• Engage with the CMA remedies team constructively and early, the reformed regime is expected to formalise earlier remedies windows during Phase II.
• Anticipate monitoring-trustee requirements and build associated costs into the transaction budget.

Deal Structuring UK, Examples and Drafting Points for PE and Mid-Market Transactions

The way a transaction is structured can materially affect CMA risk. The following techniques are particularly relevant for private equity and mid-market deal teams working within the UK merger control framework.

• Asset deal vs. share deal. An asset acquisition may allow the buyer to carve out the overlap business at signing, removing the competitive concern entirely. This is especially useful where the overlap represents a small proportion of the target’s operations.
• Conditional completion. Including a CMA clearance condition precedent, with a realistic long-stop date reflecting potential Phase II timing, protects the buyer against an adverse CMA outcome while providing the seller with deal certainty.
• Partial carve-outs. Where the competitive overlap is limited to one product line or geographic area, structuring the SPA to exclude or divest the overlap business upfront can eliminate the need for CMA notification altogether.
• Deferred consideration and escrow. Linking a portion of the purchase price to CMA clearance, through escrow or deferred-payment mechanisms, aligns financial incentives and reduces the buyer’s downside risk.
• Hold-separate provisions. Drafting robust hold-separate covenants into the SPA ensures compliance with any CMA interim measures and preserves the competitive independence of the target business pending clearance.
• Interim management arrangements. Appointing an independent manager (or monitoring trustee) to run the target business during the CMA review period can satisfy CMA concerns about pre-clearance integration while allowing the deal to proceed.

Deal structuring in the UK should be treated as a core element of merger-control strategy, not as an afterthought to SPA negotiations. Structures that are designed with CMA risk in mind from the outset avoid the costly renegotiations that arise when regulatory problems emerge after signing.

Conclusion and Next Steps

The 2026 UK merger control reform proposals do not yet change the law, but they change the operational environment in which every UK deal is planned and executed. Deal teams that wait for legislation will find themselves scrambling to meet compressed timelines and more demanding CMA expectations. Three actions should be taken immediately: first, run a competition market screen on every active deal and pipeline opportunity to identify CMA exposure; second, prepare the merger notification evidence pack during diligence, not after signing; and third, consider voluntary pre-notification for any transaction that triggers the share-of-supply test or involves a sector where the CMA has signalled heightened scrutiny.

The cost of early preparation is negligible compared to the cost of a Phase II referral or an adverse IEO imposed on a completed deal.

Sources

1. GOV.UK, Refining our competition regime (consultation)
2. Competition and Markets Authority (CMA), Merger Guidance and Notices
3. Enterprise Act 2002, legislation.gov.uk
4. Osborne Clarke, UK merger-control reform proposals raise concerns
5. Freshfields, UK Government heralds major changes to UK merger control regime
6. Pinsent Masons (Out-Law), Major UK competition law reforms proposed
7. ICLG, Merger Control Laws and Regulations United Kingdom 2026
8. Cooley, UK merger control in 2026: what to expect
9. MergerFilers, United Kingdom merger control guide