Short answer: many UK mergers do not have to be notified, but the CMA may review a transaction that satisfies any route in section 23 of the Enterprise Act 2002: target UK turnover exceeding £100 million; a share-of-supply test that creates or increases a share to at least 25%, with at least one enterprise concerned having UK turnover above £10 million; or the hybrid test, under which one enterprise concerned has at least a 33% UK share of supply and UK turnover above £350 million and another enterprise has a UK nexus. A firm designated with strategic market status, and every member of its group, must report to the CMA before completing, where an acquisition crosses the 15%, 25% or 50% qualifying-status thresholds or forms a qualifying joint venture and total consideration is at least £25 million. See Enterprise Act 2002, section 23 and DMCC Act 2024, sections 57 and 58. Last updated 12 August 2026.

The regulatory framework

UK merger control is voluntary and non-suspensory for most parties: there is no obligation to notify, but the CMA can review a qualifying merger before or after completion. A merger qualifies for review where it gives rise to a relevant merger situation under the Enterprise Act 2002, and the CMA then assesses whether it results, or may be expected to result, in a substantial lessening of competition (section 22). The substantial lessening of competition test is unchanged for digital deals. The jurisdictional thresholds in section 23 changed on 1 January 2025.

A buyer must test the deal against three routes into CMA jurisdiction, each as amended by the DMCC Act 2024. The CMA may review a deal where the target’s UK turnover exceeds £100 million; where the merger creates or enhances a UK share of supply of at least 25% and at least one enterprise concerned has UK turnover above £10 million; or where one enterprise concerned has at least a 33% UK share of supply and UK turnover exceeding £350 million and another enterprise has the required UK nexus. No relevant merger situation arises where none of the enterprises concerned has UK turnover above £10 million (section 23(2)(c)).

Routes to CMA jurisdiction for a digital or technology deal

The CMA can take jurisdiction over a digital or technology transaction by any of three routes, set out in the table below. Because market definition in digital infrastructure can be local rather than national, the share-of-supply tests can be met even where a national share looks modest, so the parties must map their actual overlaps rather than rely on headline national shares.

Route to jurisdiction	Test	Source
Target turnover	Target UK turnover exceeds £100 million	Enterprise Act 2002, section 23(1)
Share of supply	Merger creates or enhances a UK share of supply of at least 25%, and at least one enterprise concerned has UK turnover above £10 million	Section 23(2) to (4)
Hybrid	One enterprise concerned has at least a 33% UK share of supply and UK turnover above £350 million; another enterprise has a UK nexus	Section 23(4C) to (4G)
Small-merger protection	No relevant merger situation where none of the enterprises concerned has UK turnover above £10 million	Section 23(2)(c)

Reporting duties on firms with strategic market status

A firm designated with strategic market status under Part 1 of the DMCC Act, and every member of its group, has a separate pre-completion reporting duty. Under sections 57 and 58 the firm must report where a share or voting-rights acquisition in a UK-connected body corporate crosses from below 15% to at least 15%, from 25% or less to more than 25%, or from 50% or less to more than 50%, and total consideration is at least £25 million. A qualifying joint-venture formation is also reportable. The firm must not complete until the CMA has accepted a sufficient report and five working days have passed (section 63).

Why merger control matters for your deal

The parties must plan for CMA review when they set the deal timetable. The CMA can call in a completed deal and impose an initial enforcement order that freezes integration in the meantime. Parties near the thresholds routinely manage that risk through pre-notification discussions, and can now request a fast-track reference straight to a Phase 2 investigation where significant issues are likely, avoiding a Phase 1 clearance step (Enterprise Act 2002, section 34ZF). Merger review also runs in parallel with, and separately from, national security screening under the National Security and Investment Act 2021, which imposes its own mandatory notification for acquisitions of entities in the seventeen sectors specified by regulations under that Act (SI 2021/1264), among them communications and data infrastructure. Clearance under one regime cannot be assumed from the other. A buyer must plan both clearances into the deal timetable before signing.

How we work

Bratby Law acts as direct legal advisors on a specific question, as specialist co-counsel alongside a corporate team, and as fractional general counsel on a retained basis. Rob Bratby currently holds four fractional General Counsel appointments, at The One Touch Switching Company, TelXL, Core Communication and the UK Payments Initiative. On a transaction, we read the deal and the regulation together, so competition and national security clearances are handled as part of the deal rather than discovered late in it. Deal work in regulated sectors runs alongside transactions.

Frequently asked questions about merger control in digital markets

Do I have to notify the CMA before completing a deal?

For most parties, no. UK merger control is voluntary, so there is no general obligation to notify and no automatic standstill. But the CMA can review a qualifying deal after completion and freeze integration while it does, so parties near the thresholds usually notify or hold pre-notification discussions to secure certainty.

What is the new acquirer-foothold threshold?

The hybrid test is a jurisdictional route added by the DMCC Act 2024. It is met where one enterprise concerned supplies or acquires at least 33% of goods or services of a description in the UK or a substantial part of it, that enterprise has UK turnover exceeding £350 million, and another enterprise concerned has the statutory UK nexus. It does not require an overlap or increment in the 33% share.

What extra obligations apply if a party has strategic market status?

A designated SMS firm must report before completion when a UK-connected acquisition crosses the 15%, 25% or 50% qualifying-status thresholds and total consideration is at least £25 million. A qualifying joint-venture formation can also be reportable. The event cannot take place until the CMA has accepted a sufficient report and five working days have elapsed, unless the CMA consents otherwise.

How does CMA review interact with national security screening?

They are separate regimes with separate triggers and timetables. Regulations under the National Security and Investment Act 2021 specify the sectors in which notification is mandatory, among them communications and data infrastructure, and clearance under that Act cannot be inferred from CMA clearance. The parties may need both, and must plan both into the timetable.

Related digital regulation pages

The other digital regulation pages on this site:

Digital Regulation
SMS Designation and Conduct Requirements
Pro-Competition Interventions
Concurrent Competition Powers
Market Investigations and Studies
Competition Enforcement and Litigation
EU Digital Markets Act Compliance

Also see

Merger questions in regulated sectors arise alongside Transactions, Telecoms Regulation and Payments Regulation. For commentary on current developments, see our Insights.