Few Surprises, As The CMA Finalises Its Revised Approach To Merger Efficiencies

After launching a review process at the beginning of 2026, and publishing draft guidance for consultation in June, the CMA has now formalised its new approach to the assessment of efficiencies arguments in merger control cases. The new approach is set out in chapter 8 of the CMA’s revised merger assessment guidelines.

The CMA’s review of its approach to merger efficiencies was launched as part of its ongoing 4Ps initiative, aimed at improving the pace, predictability, proportionality, and process of its enforcement work.

In our previous article on this topic, we explored in detail the CMA’s draft revised guidance on the assessment of Rivalry-Enhancing Efficiencies (REEs), which took into account the feedback received in response to the CMA’s initial call for evidence. The new final guidance, which will apply to all cases in which the formal Phase 1 investigation commenced on or after the publication date of 3 September 2026, is largely unchanged from the draft version.

Below, we recap the changes that appeared in the draft guidance before exploring the noteworthy amendments that were incorporated in the final version.

Recap of the draft revised guidance

The key new elements in the draft guidance were as follows.

• A more holistic approach: the draft guidance presented a marked shift in tone, encouraging parties to come forward with REEs and committing the CMA to considering these as part of its overall assessment of the competitive impact of a merger, with no higher evidential standard being applied than for theories of harm.
• More examples of REEs: the draft guidance set out more detailed practical guidance and examples explaining situations in which REEs can arise and the types of evidence on which the CMA will focus (in particular, contemporaneous internal documents generated in the ordinary course of business).
• A broader range of possible efficiencies, namely:
  • efficiencies that do not counteract the specific harms to competition identified, but instead improve other parameters of competition;
  • dynamic efficiencies - i.e. benefits arising from increases in the merging parties' ability and incentive to compete through investment, innovation, and R&D; and
  • efficiencies that arise over different time horizons to the competitive harms identified.
• A role for behavioural remedies in securing efficiency benefits, where the CMA sees the potential for REEs but has concerns about their timeliness or likelihood.
• An emphasis on early engagement during the merger review process when raising efficiency claims - ideally during pre-notification.

Material changes between the draft and final revised guidance

Most of the changes suggested by third parties during the consultation were rejected by the CMA, with only limited amendments being made to the final guidance. We explore the more material changes below. 

Refining the assessment of internal documents 

The CMA has refined the way it describes its assessment of internal documents, with less importance being attached to when a document was produced, and a greater focus on its overall “probative value” instead. The CMA will assess this value by reference to a document’s context, purpose, and effect. 

This appears to have been prompted by concerns that the CMA would unduly place greater evidentiary weight on internal documents generated prior to contemplation of the merger than those created afterwards. However, the CMA agrees that many of the materials relevant for evidencing efficiency claims may be generated after a merger is in contemplation. The clarification of the CMA’s approach will give merging firms a somewhat greater scope to rely on documents produced during the transaction process (such as synergies analyses and transaction valuations), provided they are consistent with other contemporaneous internal documents.

Further guidance on assessing the sufficiency of merger benefits

The draft guidance noted that the CMA would consider a merging party’s track record in realising similar efficiencies in previous mergers. This has now been expanded to consider the firm’s track record in passing those benefits on to customers as well. 

Furthermore, the CMA has provided additional guidance on the evidence needed to demonstrate the type and size of the efficiencies expected to be realised. In particular, it might include evidence (e.g. in the form of survey evidence, or data on spending patterns) on how consumers value non-price benefits, or ordinary-course business plans or analyses that incorporate assumptions on future sales volumes and prices.

A little more on process

In its summary of consultation responses, the CMA stated that it did not consider that more detailed guidance on the timing of engagement was necessary, beyond what was included in the draft guidance (i.e. that firms should include an explanation of their claimed efficiencies in their Merger Notice, and that there are a range of opportunities for merger firms to engage with the CMA throughout the review process). 

However, it did strengthen the language on early engagement in the final guidance - moving from “encouraging” merging firms to engage early, to now stating that firms "should engage" early in relation to efficiency claims. This change is subtle, and was not specifically addressed in the summary of consultation responses, but further highlights the importance of engagement on efficiencies from the outset.

The CMA also noted in its summary of consultation responses that it intends to publish a template request for information on REEs, indicating the types of evidence the CMA might request during a review, and outlining some example responses. This is intended to assist parties with early engagement. The CMA will also consider whether it would be helpful to publish further examples or case studies once the final guidance has been applied in future cases.

Key takeaways

As noted above, the changes to the draft guidance are limited, and can best be viewed as refinements or clarifications rather than (further) material amendments to the CMA’s approach. Overall, the tone remains encouraging, with the CMA indicating an intention to approach arguments around efficiencies with an open mind and a willingness to consider various types of evidence.

However, as flagged in our previous article, the threshold for a successful REE claim remains high. The CMA will assess each case on its facts, and will no doubt apply a rigorous degree of scrutiny to any such arguments that are advanced. The CMA has indicated that it will include details of its analysis of efficiency claims in its published decisions - but only where that analysis formed an “important part” of its overall assessment. It may therefore be some time before the practical implications of its new approach become clear.

In the meantime, merging parties engaging in transactions where efficiencies could potentially be relevant would be well advised to raise them at the earliest opportunity, and to assemble a comprehensive evidence base that addresses the nature and significance of the benefits, and how they will be passed on to customers. 

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