CMA finalises revised merger efficiency guidance after consultation, incorporating responses from Freshfields, Linklaters, Clifford Chance and others
On 3 September 2026, the Competition and Markets Authority (CMA) published its final revised guidance on how it assesses merger efficiencies, closing a consultation that launched on 3 June 2026. The updated guidance is incorporated into the CMA's merger assessment guidelines and represents the authority's settled position on how merging parties can argue that a transaction generates efficiencies, such as cost savings or innovation benefits, sufficient to offset competitive harm. The consultation drew responses from a range of firms and organisations with direct expertise in UK merger control. Named respondents included Clifford Chance, Freshfields, and Linklaters among the law firms, alongside economic consultancies Compass Lexecon and Frontier Economics, advisory firm AlixPartners, UK Finance, the In-House Competition Lawyers' Association (ICLA), UK Private Capital, the American Bar Association (Antitrust and International Law Sections), the Association for Competitive Technology, and academics including Gregory Werden and Farasat Bokhari. The breadth of the respondent list indicates the practical significance of efficiency arguments across sectors from technology to financial services. The finalised guidance signals the CMA's current thinking on what evidence parties must produce to support an efficiency defence and how that evidence will be weighed against the competition concerns a merger raises. For deal teams advising on large UK mergers, the updated guidelines set the evidentiary benchmark for Phase 1 and Phase 2 efficiency submissions.
Why this matters
Efficiency arguments are one of the few levers merging parties can pull when facing Phase 2 scrutiny: if a transaction raises competition concerns, demonstrating that consumer benefits outweigh the harm can be the difference between approval and prohibition or remedies. Codifying the CMA's approach in updated guidelines gives deal teams and their advisers greater predictability on the standard of proof required, reducing the risk of efficiency arguments being dismissed at the margins. The involvement of Magic Circle and major US firm practice groups in the consultation confirms that the guidance matters most on the largest, most complex UK mergers where efficiency defences are most likely to be deployed.
On the Ground
Competition practices at all major UK and international law firms advising on UK mergers will need to update their Phase 2 playbooks to reflect the finalised guidance. The practical work involves reviewing the new guidelines against prior CMA decisions where efficiency arguments were accepted or rejected, and refreshing client-facing advice on the evidence threshold. On live transactions, competition lawyers will now structure efficiency claims to satisfy the new framework from the outset of deal planning rather than as a reactive response to Phase 2 concerns. A trainee on a merger clearance matter would assist with regulatory notification drafting, prepare compliance gap analysis memos comparing the transaction's claimed efficiencies against the updated CMA framework, and maintain a remediation tracker for outstanding information requests.
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