LONDON, Dec. 19, 2025 —
The UK Supreme Court has dealt a significant blow to the country’s opt-out collective actions regime, overturning a Court of Appeal ruling and confirming that the Competition Appeal Tribunal (CAT) acted within its discretion in refusing to certify a major foreign exchange (FX) damages claim on an opt-out basis.
In its judgment in UKSC 2023/0173, the court upheld the CAT’s decision to deny certification of collective proceedings brought on behalf of businesses affected by unlawful FX trading conduct, despite the claims being follow-on actions from European Commission infringement decisions against major banks. The Supreme Court found that the CAT was entitled to conclude that the claim was weak, primarily because it was not persuaded by the causal link between the cartel conduct in trader chatrooms and alleged market-wide harm.
In a ruling with wide implications for collective litigation, the Supreme Court held that “if a claim is weak, that militates against affording claimants the advantages of an opt-out process,” effectively introducing a more demanding merits-based assessment at the certification stage. This is the case even where claims are not struck out and defendants have not applied for summary dismissal.
The court also clarified the role of practicability in determining whether proceedings should be opt-in or opt-out. It said that where it is practicable for claimants to bring opt-in proceedings—such as large businesses with substantial individual claims—opt-out proceedings are unlikely to be proportionate. By contrast, opt-out actions remain appropriate for mass consumer claims involving small individual losses. In cases falling between these extremes, the CAT must make an objective assessment of class composition.
In the FX case, the presence of a small number of large claimants was enough to rule out opt-out certification, notwithstanding the existence of large numbers of small and medium-sized enterprises for whom individual litigation would be impractical.
While the Supreme Court confirmed that opt-in and opt-out decisions ultimately remain within the CAT’s discretion, it did so within what practitioners say are now narrower and less certain boundaries. Critics argue the ruling leaves UK SMEs without effective redress, even as similar claimants in the US and large European institutions have recovered damages for the same infringements.
The judgment is expected to intensify calls for legislative reform, with pressure mounting on the government to revisit the opt-out regime as part of its ongoing review of private enforcement and access to justice in competition cases.
