UK Law and Practice Contributed by: Samantha Ward, Ben Jasper, Ryan Byrne and Chloe Lettington, Clifford Chance LLP
• whether disclosure would increase leniency appli - cants’ liability exposure or disadvantage them rela - tive to non-cooperating parties; • whether it would deter potential future leniency applicants; and • whether the disclosure sought was proportionate. The EC intervened against disclosure of leniency documents; the judge assessed relevance on a doc - ument-by-document basis and ordered only limited disclosure.
pense with hearing oral evidence if a written witness statement suffices or it may limit cross-examination of witnesses. The CAT also has the power to issue a summons requiring a person in the UK to attend as a witness before the CAT and produce documents. The CAT’s 2021 practice direction (Practice Direction 2/2021) on witness statements for trial provides that a statement must contain only evidence of fact needed to be proved at trial on an issue to be decided, limited to matters about which the witness would be asked and allowed to give in evidence-in-chief if called oral - ly. The witness statement must set out only matters of fact within the witness’s personal knowledge that are relevant to the case and must list any documents referred to in preparing it. Both the witness and legal representative must sign a statement of compliance. 7.2 Expert Witness Role and Procedure Expert evidence in the High Court requires the High Court’s permission and follows the exchange of fac - tual witness statements. The expert’s duty to the court overrides any obligation to the instructing party. Evi - dence is normally given in a written report, followed by written questions and possible cross-examination at trial. The court may order joint statements clarify - ing areas of agreement and disagreement before trial or may order the appointment of a single joint expert (although this is less common in antitrust claims). There have also been cases where courts have ordered that expert evidence be given concurrently, also known as “hot-tubbing”, which is typically judge- led and results in more limited time for cross-examina - tion by the parties (recently in National Grid Electricity Transmission plc v ABB Ltd ). The CAT also has similar rules for dealing with expert evidence (see, in particular, the CAT’s Practice Direc - tion 3/2025) and may also appoint its own expert.
7. Witness and Expert Opinions 7.1 Witness Procedure High Court
Factual evidence in the High Court may take the form of documents or witness evidence. Witness evidence is provided in witness statements (which are exchanged in advance of trial) and oral evidence given at trial. A witness may be cross-examined and re-examined at trial on the basis of their witness statement. The weight given to witness evidence will depend on the credibility of the witness, as well as on the other cir - cumstances of the case. A party wishing to secure the evidence of a witness present within the jurisdiction, in the form of oral evidence at trial, can also issue a witness summons under CPR 34.31. In the business and property courts, Practice Direction 57AC applies to trial witness statements. The require - ments include that a trial witness statement must: • contain only evidence of fact needed at trial on an issue to be decided at trial; and • set out only matters of fact within the witness’s personal knowledge that are relevant to the case. CAT The CAT proceeds on the basis that it will “be guided by overall considerations of fairness rather than tech - nical rules of evidence” ( Argos v OFT (2003) CAT 16). The CAT has the general power to control the evi - dence placed before it by giving directions as to the issues on which it requires evidence, the nature of the evidence it requires, and the way in which the evi - dence is to be placed before it. The CAT may also dis -
230 ANTITRUST LITIGATION 2026
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