The Competition and Markets Authority (CMA) opened a public consultation on its draft revised guidance for assessing rivalry‑enhancing merger efficiencies at 11 am on 3 June 2026, and will accept comments until 5 pm on 1 July 2026 CMA source. The consultation window, lasting just under a month, gives businesses, advisers and consumer groups a narrow period to influence the final rules that will shape how future mergers are evaluated for efficiency gains.
Why the guidance is being revised
In January 2026 the CMA launched a review of its approach to assessing rivalry‑enhancing efficiencies in mergers. The review was intended to address concerns that the existing framework did not adequately capture the competitive benefits that can arise when merging firms achieve cost savings, productivity gains or other efficiencies that benefit consumers. The outcome of that review is the draft revised guidance published on the same day the consultation opened, 3 June 2026 CMA source.
Key dates in the consultation process
| Event | Date & time (GMT) |
|---|---|
| Consultation opened | 3 June 2026 – 11:00 |
| Consultation closed | 1 July 2026 – 17:00 |
| Outcome published | 3 September 2026 |
| Source: Competition and Markets Authority – Draft revised guidance on our approach to assessing merger efficiencies | |
The table summarises the three milestones that are already fixed in the CMA’s schedule. The outcome, expected on 3 September 2026, will incorporate any substantive changes resulting from the consultation period.
What the draft guidance covers
The draft guidance sets out a refreshed methodology for evaluating efficiency arguments that a merger may present. It clarifies three core elements:
- Definition of rivalry‑enhancing efficiencies: the guidance narrows the scope to efficiencies that are likely to improve consumer welfare without substantially lessening competition.
- Quantitative thresholds: it proposes specific thresholds for cost‑saving estimates, requiring firms to demonstrate that the savings are both credible and likely to be passed on to customers.
- Timing of benefits: the guidance asks parties to show when the efficiencies will materialise, distinguishing short‑term gains from longer‑term structural benefits.
All three points are drawn directly from the CMA’s consultation page, which explains that the revised approach is intended to make the efficiency test more transparent and predictable for market participants CMA source.
For companies planning mergers, the consultation period is the only window to shape the final guidance. Submissions can influence how strictly the CMA will scrutinise efficiency claims, potentially affecting deal timing, structure and the need for divestitures. Legal and economic advisers are likely to prepare detailed comment letters that reference case law, industry data and the CMA’s own previous guidance from 2024.
Because the consultation closes on 1 July 2026, firms with merger proposals slated for the second half of 2026 will need to anticipate the final rules when they file their merger notices. If the CMA adopts stricter thresholds, some deals may require additional evidence of consumer benefit or may be re‑shaped to meet the new criteria.
Who can comment and how
The CMA invites comments from any interested party – including merging firms, competitors, consumer groups, trade associations and academic experts. Submissions are made through the GOV.UK consultation portal, where the CMA provides a template for responding to each of the three core elements of the draft guidance. The portal also records the date and time of each submission, ensuring a transparent audit trail CMA source.
What remains unknown
The CMA has not disclosed how many responses it expects, nor the proportion of comments that will come from large multinational firms versus smaller domestic players. It also has not indicated whether the final guidance will include any new quantitative thresholds beyond those outlined in the draft. Market participants should therefore monitor the 3 September 2026 outcome publication for any surprise adjustments that could affect pending merger filings.
Next steps after the consultation closes
Once the 5 pm deadline on 1 July 2026 passes, the CMA will review all submissions, assess the weight of evidence and incorporate any agreed‑upon changes into the final revised guidance. The final document, expected on 3 September 2026, will replace the 2024 guidance and become the benchmark for assessing rivalry‑enhancing efficiencies in all future merger cases.
Stakeholders with ongoing or planned merger transactions should therefore use the remaining weeks to submit detailed, data‑driven comments, ensuring that any efficiency arguments they intend to rely on are aligned with the draft’s proposed thresholds and definitions.