Authors Anca Cojoc and Nikita Roketskiy discuss the UK’s Competition Appeal Tribunal (CAT)’s comprehensive guidance on expert witnesses in competition litigation in “The Road Ahead After the UK CAT Practice Direction.”
In December 2025, the CAT issued a comprehensive Practice Direction on Expert Evidence, providing detailed guidance on the role and conduct of expert witnesses in competition litigation. This article discusses the key lessons and practical challenges arising from this new guidance as it relates to economic evidence. The new guidance from the CAT represents a renewed focus on how testifying economists develop and present economic evidence. The themes of greatest interest that emerge from the Practice Direction and recent CAT judgments include the necessity of fact-based modelling, the push for methodological transparency, and the CAT’s active intervention to prevent advocacy.
The new guidance from the CAT represents a renewed focus on how testifying economists develop and present economic evidence.
Key Discussion Points
- The need to calibrate quantitative models to observed factual evidence
- The challenges of ex-ante model specification in applied econometrics, which is inherently iterative
- The implications of disclosing unfavourable initial analyses and the difficulty of distinguishing outcome-driven model selection from routine model selection
- The tension between relying on established economic methodologies and the need for case-specific evidential foundations
This article was originally published by Global Competition Review’s Europe, Middle East and Africa Antitrust Review in June 2026.
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