CMA Market Definitions

Post-Brexit UK competition law market definitions — from the Competition and Markets Authority

About Competition and Markets Authority

The Competition and Markets Authority (CMA) is the UK's primary competition and consumer authority, created in 2014 and now operating fully independently from EU merger control following Brexit. Since January 2021, the CMA has developed a standalone body of market definition precedent across UK domestic and internationally significant transactions. It has emerged as one of the world's most active and interventionist authorities, particularly in digital markets.

Why CMA Market Definitions Matter

  • Post-Brexit, the CMA has sole jurisdiction over mergers with a UK dimension — EC clearance no longer covers the UK, making CMA precedent mandatory for any deal with UK activities
  • CMA Phase 1 and Phase 2 decisions contain highly detailed market definition analysis, particularly in digital markets, pharma, and grocery retail
  • The CMA has frequently diverged from EC findings on digital and tech mergers, making its independent market definitions essential reading for international M&A teams

Frequently Asked Questions

What is the CMA?

The Competition and Markets Authority (CMA) is the UK's independent competition and consumer authority, headquartered in London. Created by the Enterprise and Regulatory Reform Act 2013 (replacing the OFT and Competition Commission), it has had sole jurisdiction over UK merger control since the UK's exit from the EU on 1 January 2021.

How does CMA merger control differ from the European Commission post-Brexit?

Following Brexit, transactions that previously received a single EC clearance now require separate review by both the EC (for EU dimension) and the CMA (for UK dimension). The CMA applies UK domestic tests — a 25%+ combined UK share of supply, or UK turnover of the target above £70m — and is not bound by EC precedent, though it draws on it regularly.

What is the CMA Phase 1 and Phase 2 process?

CMA merger review has two phases. Phase 1 is an initial 40-working-day review assessing whether a 'realistic prospect' of substantial lessening of competition exists. If concerns are found, the transaction enters Phase 2 — an in-depth 24-week investigation by an independent panel, including detailed market definition analysis supported by economic evidence.

Is CMA precedent relevant for EU merger filings?

Yes, though CMA and EC are not bound by each other's decisions. For cross-border mergers requiring notifications in both jurisdictions, CMA market definitions are directly relevant and often cited in EC proceedings. Post-Brexit divergence between CMA and EC findings has increased, particularly in digital markets such as the Meta/Giphy and Microsoft/Activision reviews.