UK CMA Finalizes Revised Merger Efficiencies Guidance Following Consultation Closure

Key Takeaways

• The UK Competition and Markets Authority (CMA) has concluded its consultation and published final revised guidance on assessing rivalry-enhancing efficiencies in mergers, now incorporated into its updated Merger Assessment Guidelines.
• Compliance and legal teams advising on UK transactions should review the final text, because it changes how efficiency arguments are framed and evidenced in merger reviews.

Deep Dive

The CMA ran the consultation from 3 June 2026 to 1 July 2026 and published the final outcome on 3 September 2026. The final guidance replaces the text in paragraphs 8.2 to 8.27 of the Merger Assessment Guidelines. It follows a review launched in January 2026 and forms part of the CMA's broader work to embed its 4Ps framework (pace, predictability, proportionality, and process) in merger control. Final guidance is a 10-page document, with a 12-page summary of consultation responses and a 29-page consultation document explaining the proposed changes.

The source material does not describe the substantive changes in the final text, so the specific revisions to evidentiary standards or the treatment of efficiencies cannot be confirmed from this update alone. Given the 4Ps emphasis, teams should expect a focus on greater predictability and proportionality in how parties present, and the CMA evaluates, rivalry-enhancing efficiencies. Respondents included major law firms (Clifford Chance, Freshfields, Linklaters), economic consultancies (Compass Lexecon, Frontier Economics, AlixPartners), industry bodies (UK Finance, UK Private Capital), and the ABA. This suggests the changes are relevant to financial services and private capital transactions. Teams should read the final guidance and the response summary directly to identify differences from the draft.

No separate implementation deadline is stated, and the guidance is described as already incorporated into the updated guidelines. Teams should therefore assume it applies to merger reviews going forward, and confirm the effective date and any transitional treatment of ongoing cases in the full publication.

Recommended actions: - Obtain and review the final guidance and compare it to the June draft. - Update internal merger-control playbooks, deal checklists, and templates for efficiency submissions. - Brief M&A, legal, and economics advisers on the changes. - Reassess the evidence needed to support efficiency claims, such as quantification, verifiability, and pass-through to customers, in pending and planned UK transactions. - Consider early engagement with the CMA, including pre-notification discussions, on efficiency arguments.

Risk implications are moderate. Poorly evidenced or outdated efficiency arguments may weaken a party's position in Phase 1 or Phase 2 reviews, leading to delays, remedies, or prohibition. Well-prepared submissions that follow the new framework may improve timing and predictability. Organizations active in UK financial services M&A should monitor how the CMA applies the guidance in early cases.

Source: Competition and Markets Authority