Notify the CMA or Complete the Deal Without Telling Them? Pre‑notification vs No‑notification (UK, 2026)

Every UK‑relevant merger forces the same binary question: should the deal team notify the CMA vs complete without notification before closing the UK merger? Unlike most major jurisdictions, the United Kingdom operates a voluntary merger‑control regime, there is no legal obligation to file. That freedom creates a genuine strategic choice, and in 2026 it carries higher stakes than ever. The CMA’s accelerated Phase‑1 targets, expanded use of legally binding commitments, and willingness to call in completed deals mean the timing, cost and deal‑certainty trade‑offs have shifted materially. This guide maps those trade‑offs dimension by dimension and delivers a concrete decision framework for in‑house counsel, PE sponsors and M&A leads with a live transaction.

Option A: Pre‑Notify the CMA

Pre‑notification is the voluntary route by which merging parties submit a merger notice to the Competition and Markets Authority under Part 3 of the Enterprise Act 2002. The CMA then assesses whether the transaction is likely to result in a substantial lessening of competition (SLC). Although the process adds weeks to the pre‑close timeline, it buys something no contractual clause can replicate, regulatory certainty before funds change hands.

What pre‑notification achieves

Filing before completion locks in three advantages:

• Early engagement. The CMA’s case team reviews internal documents, market data and the parties’ competitive assessment before the deal closes, reducing the risk of a surprise investigation later.
• Remedy negotiation on your timetable. If overlaps are identified, the parties can offer binding commitments, structural or behavioural, and negotiate terms while they still control the transaction structure. Early indications suggest this route increasingly produces tailored remedies rather than outright prohibition.
• Faster path to business certainty. A Phase‑1 clearance (or clearance subject to undertakings) gives lenders, shareholders and integration teams the green light without post‑close regulatory uncertainty.

Practical steps and timeline to pre‑notify

Deal teams typically begin with informal pre‑notification discussions, sometimes called “pre‑notification engagement”, in which the CMA case team scopes the information requirements before the formal merger notice is submitted. The formal notice itself (often referred to as CMA2) triggers the Phase‑1 statutory clock. Teams should budget for document collation, market‑share analysis and internal decision‑document review before submission. The CMA encourages parties to engage early, and its published guidance sets out confidentiality protocols for protecting deal‑sensitive material during the process. When pre‑notification discussions and the formal notice are well prepared, the combined elapsed time from first contact to Phase‑1 clearance can fall comfortably within a standard SPA long‑stop date.

Option B: Complete the Deal Without Notifying the CMA

Because UK merger control is voluntary, parties can sign and close without any regulatory filing. Many transactions, particularly those with limited UK customer overlap or modest combined market shares, complete this way every year without incident. The risk, however, is not zero: the CMA retains the power to investigate completed mergers and, if an SLC is found, to order remedies up to and including unwinding the deal.

How the CMA can call in completed mergers

Under the Enterprise Act 2002, the CMA may open a merger investigation on its own initiative. It monitors market intelligence, press reports, third‑party complaints and its own merger‑intelligence function to identify completed mergers that may raise competition concerns. Once the CMA is aware of a completed merger, it has a four‑month window from the point at which the merger was made public (or the CMA was otherwise made aware) in which to refer the case for a Phase‑2 investigation. Transactions that escape this window without a reference are generally safe from further CMA action, but the clock only starts once the CMA has sufficient information, so quiet completions can leave the window open for an extended period.

Practical mitigation steps when completing without notification

Deal teams that accept the call‑in risk should build protections into the transaction documents:

• Regulatory‑risk holdbacks or escrow. A portion of the purchase price is held back pending expiry of the CMA call‑in window.
• Warranties and indemnities. The seller warrants competition‑law compliance and indemnifies the buyer for CMA‑related costs or remedy losses.
• Separation and information protocols. Parties may agree operational ring‑fencing so that an unwinding order, if issued, can be implemented without destroying the business.

Notify the CMA vs Complete Without Notification, Side‑by‑Side Comparison

The table below maps the core decision dimensions. Use it as a quick‑scan reference before reading the detailed analysis that follows.

The core trade‑off is straightforward. Pre‑notification exchanges upfront time and cost for deal certainty and strategic control over remedies. Completing without notification preserves speed but transfers regulatory risk downstream, where it is harder to manage and more expensive to resolve.

For deals with material UK overlaps or regulatory‑sensitive sectors, the balance tilts decisively toward pre‑notification. For transactions with a genuinely limited UK footprint and low SLC probability, completing without notification can be a rational choice, provided the deal documents include adequate protections.

Dimension‑by‑Dimension Analysis

Timing: CMA Phase‑1, Phase‑2 and accelerated pathways

The CMA timeline is the single most important variable for deal structuring. Understanding the formal clock is essential for setting SPA long‑stop dates and financing conditions.

The CMA’s 2025–26 operational targets signal a push toward faster Phase‑1 resolution where parties engage early and provide complete information. Industry observers expect this trend to continue, making well‑prepared pre‑notifications comparatively faster than in previous years.

Cost: CMA merger notice cost, counsel fees and remedy negotiation

The CMA does not charge a fixed filing fee for voluntary merger notices. The primary costs are external competition counsel and, where remedies are negotiated, the commercial cost of commitments. The table below illustrates typical ranges.

The key insight on cost is asymmetric risk: pre‑notification costs are predictable and front‑loaded, while the costs of a post‑close call‑in are unpredictable, reactive and almost always higher per pound of counsel time.

Liability, enforcement and call‑in risk

The CMA’s call‑in power under the Enterprise Act 2002 means that completing without notification never eliminates regulatory risk entirely, it merely defers it. If the CMA identifies a completed merger that raises SLC concerns, it can issue an initial enforcement order (IEO) to prevent further integration while it investigates. Post‑investigation remedies can include mandatory divestment, behavioural undertakings, or, in the most serious cases, an order to unwind the transaction. The CMA’s clearance of the Vodafone/Three merger subject to legally binding commitments in 2024–25 illustrates the regulator’s willingness to attach enforceable conditions even to cleared mergers.

Enforceability and remedies: binding commitments vs blocked merger

Binding commitments (also called undertakings in lieu of reference, or UILs) are legally enforceable obligations that the merging parties accept in exchange for the CMA clearing the deal without a full Phase‑2 investigation. They may include structural remedies (divestment of business units or assets) or behavioural commitments (access obligations, pricing controls, service guarantees). The CMA monitors compliance and can take enforcement action for breach. The likely practical effect of the CMA’s increased reliance on binding commitments is that well‑advised parties who pre‑notify can negotiate proportionate remedies, while parties who are called in after completion face remedies imposed under time pressure with less scope for tailoring.

Deal certainty and commercial consequences

For PE sponsors with fund‑life constraints and sellers with price‑certainty expectations, regulatory risk is not abstract, it affects deal economics directly. Pre‑notification allows the SPA to be conditioned on CMA clearance, giving both sides a known exit if the regulator objects. Without notification, the buyer carries latent regulatory risk that may surface months after closing, potentially triggering indemnity claims, earn‑out disputes or write‑downs. Lenders increasingly require either regulatory clearance or enhanced covenant packages before drawdown, making pre‑notification a practical financing prerequisite in many leveraged transactions.

What Changes in 2026: The CMA’s Operational Shift

Two developments in 2025–26 have reset the pre‑notification vs no‑notification calculation. First, the CMA has signalled, and operationally delivered, faster Phase‑1 resolution for parties that engage early and provide complete, high‑quality submissions. Second, the CMA has demonstrated a clear preference for resolving competition concerns through binding commitments rather than proceeding to Phase‑2 where feasible, as illustrated by the Vodafone/Three clearance subject to legally binding commitments.

For deal teams, this means that pre‑notification is no longer synonymous with delay. Early engagement can compress the combined pre‑notification‑plus‑Phase‑1 window, and the increased availability of binding commitments means that many deals that would previously have faced Phase‑2 referral can now be resolved at Phase‑1, provided the parties come prepared with credible remedy proposals. The corollary is that completing without notification in a deal with real UK overlaps is riskier than before: if the CMA calls in the transaction, the same binding‑commitment framework applies, but the parties negotiate from a weaker position because integration has already begun.

Decision Framework: When to Pre‑Notify the CMA vs Complete Without Notification

The table below maps common deal profiles to the recommended path. Use it alongside competition counsel’s assessment of your specific market overlaps and SLC risk.

Choose pre‑notification (Option A) when:

• Combined UK market shares or overlaps are material in any national or local market, or the sector attracts CMA scrutiny (telecoms, pharma, energy, transport, defence).
• Financing conditions require regulatory clearance or the SPA long‑stop date accommodates a Phase‑1 window.
• The deal team wants to shape remedies proactively and preserve commercial value through negotiated binding commitments.
• The seller requires cleared‑deal certainty to accept the purchase price without holdback or escrow discounts.

Choose completing without notification (Option B) when:

• Preliminary screening shows a genuinely limited UK footprint and low SLC probability, the transaction does not trigger the CMA’s jurisdictional thresholds or raises only de minimis overlaps.
• Time to close is essential (e.g., distressed sale, auction with a hard deadline) and all counterparties accept the regulatory contingency with appropriate contractual protections.
• The commercial risk of a post‑close call‑in has been quantified, insured or allocated through warranties, indemnities and escrow arrangements.

When to Engage a Competition Lawyer for This Decision

The question of whether to notify the CMA vs complete without notification in a UK merger is not one to resolve on instinct. Competition counsel should be retained, ideally before signing, whenever any of the following triggers are present:

• Market overlap flags. Preliminary analysis shows the merging parties both supply the same product or service to UK customers, or a vertical relationship creates potential foreclosure concerns.
• Material UK turnover. Either party’s UK turnover exceeds the CMA’s jurisdictional threshold, or the combined entity’s share of supply in any UK market is or may be 25% or more.
• Financing conditioned on clearance. Lenders or equity investors require regulatory sign‑off as a condition precedent to drawdown.
• Remedies are likely. The deal involves a sector with recent CMA enforcement activity, or internal analysis suggests overlaps that could attract binding commitments.
• Reputational or public interest considerations. The transaction touches a politically sensitive sector, involves media scrutiny, or may trigger a public interest intervention notice.

In the first 48–72 hours of engagement, counsel should conduct a rapid jurisdictional screen, prepare a preliminary SLC assessment, advise on SPA conditionality and, if pre‑notification is recommended, begin drafting the pre‑notification engagement letter to the CMA.

Sources

1. GOV.UK, Tell the CMA about your merger
2. CMA, A quick guide to UK merger assessment (CMA18)
3. GOV.UK / CMA, Merger Assessment Guidelines
4. Enterprise Act 2002
5. GOV.UK, CMA clears Vodafone/Three merger subject to legally binding commitments