The £14 Billion Dilemma: UK Courts Clash With Complex Economic Evidence

LONDON, UK – September 30, 2026 – In the high-stakes arena of UK competition litigation, a quiet but profound collision is occurring. On one side, an unprecedented wave of mega-value collective actions is sweeping through the courts, with claims that once peaked at a staggering £1 billion now routinely ballooning to an astronomical £14 billion. On the other side, the UK judiciary is increasingly laying down the law on procedural efficiency, demanding that the sprawling, labyrinthine economic evidence required to prove such claims be radically streamlined.

This escalating tension is the focal point of a newly released report by Cornerstone Research, a global economic and financial consulting firm. The study, which draws on candid interviews with prominent competition litigators from elite law firms including CMS, Freshfields, Linklaters, and Quinn Emanuel, captures a critical inflection point for the UK class action regime. As the Competition Appeal Tribunal (CAT) tightens its grip on procedural rules, the legal and financial ecosystems surrounding these massive disputes are being forced to adapt or face devastating courtroom defeats.

The Proportionality Push: Efficiency Versus Rigor

The UK's collective redress regime has matured rapidly since the Consumer Rights Act 2015 introduced an "opt-out" mechanism for UK-domiciled claimants. This legislative shift opened the floodgates for large-scale consumer actions, transforming the CAT into one of the most vital—and busiest—judicial bodies in Europe. However, as the scale of litigation has grown, so too has the tribunal's intolerance for protracted, overly academic proceedings.

Recent procedural updates, notably the CAT's Practice Direction 2/2025, have enforced strict page limits and rigid proportionality standards on expert reports. For economists and financial consultants tasked with modeling counterfactual market scenarios spanning decades and millions of consumers, these constraints present a formidable challenge. Practitioners are increasingly questioning how demands for shorter reports and simplified analysis can be reconciled with genuinely complex economic realities.

The tribunal's intensifying scrutiny is not merely a matter of formatting. Judges are actively challenging what they perceive as abstract, dogmatic, or partisan economic modeling. Landmark proceedings, such as the ongoing Merricks v Mastercard litigation and the Justin Gutmann v Apple Inc. case, have served as highly public arenas for this judicial pushback. In these instances, the CAT has rigorously examined the methodologies proposed for assessing aggregate damages, frequently demanding revisions and demonstrating a stark refusal to accept advocacy masquerading as objective expert evidence.

Liam Colley, senior vice president and head of Cornerstone Research's European competition practice, notes that the tribunal's approach should not be misinterpreted. "The CAT has been dealing with complex economic issues since its inception in 2003 and has a huge amount of sophistication and judgement," Colley explained. "What has changed since the introduction of the class action regime is not the sophistication required, but the sheer scale of what is now at stake in a single case. Claims that would once have been considered exceptional at £1bn have given way to claims of £14bn—an unprecedented figure."

He added a crucial caveat for practitioners: "It would be a mistake to confuse the Tribunal's pragmatism with an invitation to shy away from doing the complicated economic analysis. The Tribunal is not asking experts to simplify their analysis—in fact, it is being very demanding about what's going to pass muster. There aren't shortcuts that experts can take. They have to apply the tools effectively, grounded in the factual matrix, however complex, and explain all that as clearly as they can."

A Shifting Regulatory and Funding Landscape

The friction within the courtroom is rippling outward, impacting the broader business ecosystem that finances and supports these mammoth legal battles. Third-party litigation funding is a cornerstone of the UK's opt-out class action regime, providing the immense capital required to take on global corporations. However, the CAT's rigorous evidentiary demands are fundamentally altering the risk calculus for these investors.

Litigation funders are now conducting unprecedented levels of due diligence on the economic merits of proposed cases. The heightened risk of a Collective Proceedings Order (CPO) being rejected—or a quantum assessment being drastically reduced due to insufficient or overly complex economic evidence—directly threatens their return on investment. Consequently, funders are placing a massive premium on legal teams that can secure top-tier economic experts capable of navigating the CAT's scrutiny.

Adding to this climate of uncertainty is the UK Government's latest consultation on competition redress reform, which formally closed just days ago on September 25, 2026. Spearheaded by the Department for Business and Trade, the consultation sought to evaluate the effectiveness of the current framework, probing highly contested issues such as the appropriateness of the opt-out regime, the regulation of litigation funders, and methodologies for distributing damages.

The submissions reflect a deeply divided landscape. Claimant bodies and consumer advocacy groups have fiercely defended the opt-out mechanism, arguing it is the only viable path to hold corporate giants accountable for widespread, low-value consumer harm. Conversely, defense lobbies and corporate interest groups have pushed for reforms that would introduce greater certainty, curb the influence of litigation funders, and provide robust protections against what they characterize as speculative "strike suits." The impending legislative response to this consultation could fundamentally rewrite the rules of engagement for future mega-claims.

The Evolution of the Expert Witness

As the legal and regulatory goalposts shift, the market for expert witnesses is undergoing its own rapid evolution. Technical brilliance and academic pedigree, while still foundational, are no longer sufficient to guarantee success in the CAT. Today's economic experts must be elite communicators, capable of distilling incredibly dense econometric data into lucid, compelling narratives that resonate with a non-expert tribunal.

Law firms are adapting by engaging economic consultants much earlier in the litigation lifecycle. Rather than bringing experts in to validate a pre-existing legal strategy, litigators are using economic analysis to shape the case theory from inception, ensuring that the core arguments can be robustly proven within the CAT's proportionate evidence constraints. Some legal teams are even pioneering "modular" reporting strategies—presenting streamlined core arguments within the tribunal's page limits, supported by highly technical appendices available upon request.

Furthermore, the CAT's frequent use of "hot-tubbing"—a process where opposing experts give evidence concurrently and are questioned together by the judge—has placed an extraordinary premium on an expert's ability to think quickly, maintain objectivity under pressure, and clearly articulate points of agreement and divergence. The tribunal's vocal criticism of witnesses deemed overly partisan has sent a clear message: credibility is the ultimate currency.

This shifting paradigm has exposed a pressing need to broaden the existing talent pool. As the volume and value of collective proceedings continue to climb, the industry faces an urgent imperative to develop the next generation of testifying economists. Cultivating experts who possess the rare combination of rigorous analytical skills, unshakeable independence, and masterful courtroom communication will be essential for both claimant and defense teams navigating the increasingly perilous waters of UK competition law.

Ultimately, the findings from the recent consulting report illuminate a legal system striving to balance the scales of justice with the practical realities of modern litigation. As claims stretch into the tens of billions, the UK courts are drawing a line in the sand, demanding that the economics underlying these historic disputes be as transparent and accessible as they are rigorous. For the lawyers, funders, and experts operating in this high-stakes arena, mastering this difficult balance is no longer just a procedural preference—it is the prerequisite for survival.