The Quiet Revolution In The CMA's Assessment Of Local Mergers – Yet More Substantial Local Complexity

U.K. merger control has experienced material shifts in the last few years, particularly in how the CMA approaches its assessment of local mergers. This is notable as, in the five years to April 2025, almost half (43%) of all Phase I CMA SLC findings involved local mergers, covering a veritable A to Z of activities, such as aggregates, betting shops, circular ducts and fittings, dental services, groceries, student accommodation, and veterinary practices. This makes CMA clearance a clear hurdle in business acquisition plans.

In the latest expert chapter for ICLG's Merger Control 2026 report, Alessandro Faraguna, Ben Forbes, Mat Hughes, and Caitlin Wilkinson from AlixPartners' Economics team draw insights from the more recent merger cases reviewed by the CMA.

The full chapter is available below. In summary:

• The CMA's decisional practice has shifted significantly. Since the 2021 Revised Merger Assessment Guidelines, the CMA increasingly relies on mechanistic decision rules – i.e. threshold-based tests (often market share or competitor counts) – rather than bespoke analysis in individual local areas. Nearly 70% of local cases since 2021 used decision rules.

• This shift matters as local competition dynamics are nuanced – catchment areas and competitive effects may vary locally due to geography (roads, traffic, etc.), customer behaviour, and store characteristics – yet decision rules often reduce these complexities to a single threshold.

• Common decision rule thresholds are now lower than historically seen. Local decision rules often start at a c.30-35% combined market share with a 5% increment, notably lower than typical non-local share benchmarks for SLC findings of 40% plus. (Like all generalisations, there are exceptions.)

• The CMA has opted for decision rules even in the same industries where it had previously run filters/detailed competition assessments, and in cases involving only a small number of local areas giving rise to SLC findings (e.g., fewer than five). While a more consistent use of decision rules may help in the CMA's "predictability" objective, in certain cases – particularly those with few local overlaps – this may come at the expense of proportionality, namely limiting remedies to where they are needed. However, in a select number of cases, the CMA may adopt a filtering rule followed by a detailed local assessment. Also, even when adopting a decision rule, the CMA has picked different concentration measures, but with some evidence of a preference for market shares (or market share-based proxies).

• For businesses, the lesson is clear: anticipate scrutiny early and be prepared for some degree of uncertainty at the merger clearance stage. Robust location data, accurate catchment analysis, and sensitivity testing are crucial for forecasting risk and preparing effective remedies. At AlixPartners, we have developed a market-leading automated tool to capture the full range of possible sensitivities, allowing merging parties to easily visualise the different possible outcomes under various assumptions.

Since finalising the chapter, the CMA has cleared the acquisition of Empiric by Unite Students, a student accommodation provider. In its Phase I investigation, the CMA did not adopt a decision rule route and instead ran a filtering rule followed by a detailed local assessment of certain areas – consistently with case precedent in the sector. This further highlights the importance of highlighting the sensitivities and nuances that a local competition assessment warrants. Clarity on these issues was facilitated by the CMA being given an AlixPartners' "dashboard" tool, which allowed the CMA to review and adjust the assessment of local competition issues across multiple overlapping areas and capture differences in local factors that affected local rivalry.

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