Braunford LLP & Anor v Pierre Allain

Issues for disclosure must identify the documentary material needed for a fair and proportionate trial. They should be focused, non-overlapping and framed by the real factual disputes, rather than by an unduly granular list of trial issues.

Expert evidence is admitted only where there is recognised expertise, a suitably qualified witness, and evidence that is necessary, helpful and reasonably required in the proceedings. Pure questions of fact ordinarily fall to be decided on factual evidence. In confidential-information litigation, however, expert evidence may reasonably be required where confidentiality restrictions impede factual evidence about the practical utility of the information to a hypothetical competitor. Proportionality, equality of arms, cost and expedition may justify a single joint expert.

The claimants alleged that the defendant, a former data scientist, had copied confidential information and trade secrets concerning quantitative trading strategies before joining a competitor. The case was subject to an expedited trial and confidentiality arrangements.

At a case management conference, the court determined outstanding disclosure issues and the defendant’s application for permission to rely on expert evidence concerning trading-strategy development, public-domain knowledge, valuation, retention of value and practical utility. The central questions were whether proposed disclosure was necessary and proportionate, and whether expert evidence was reasonably required to resolve issues bearing on liability and injunctive relief.

1. Disclosure. Issues for disclosure are distinct from issues for trial. They should be limited to the key factual issues requiring extended disclosure, avoid duplication and excessive granularity, and be assessed by reference to the documents likely to exist and their probative value. The proposed issues concerning trading-strategy stages and work on Humber by teams excluding the defendant were refused. They were either duplicative or irrelevant to the true focus of the litigation, namely the confidential material accessed and misappropriated by the defendant. The risk that disclosure would give the defendant access to further confidential information was an additional proportionality consideration.
2. The defendant’s email accounts, including accounts created after commencement of the proceedings, were to be searched for non-privileged disclosable material. The duty of disclosure was continuing, and post-litigation evidence of misuse could be relevant to the relief issue.
3. Expert evidence. The sequential inquiry was whether expert evidence was necessary; if not, whether it would assist the court; and, if so, whether it was reasonably required in the proceedings having regard to proportionality, cost, delay, the value and importance of the claim, and the effect on the parties. The burden of establishing admissibility and reasonable necessity rested on the party seeking permission.
4. Expert evidence was refused on trading-strategy stages, public-domain or industry knowledge, valuation and retention of value. Those matters could be determined on factual evidence, and financial value was not necessary to establish breach of confidence or copyright because secrecy and inaccessibility could themselves provide commercial value.
5. Permission was granted for a single joint expert on whether the copied information would assist a hypothetical competitor to develop or duplicate a trading strategy, and, if so, in what circumstances, to what extent and for how long. Such evidence was not strictly necessary, but would materially assist in determining the nature and duration of any injunction. Equality of arms, proportionality, timing and cost supported a single joint expert.

The parties were invited to agree an order giving effect to the judgment.

First-instance case management decision. The judgment records earlier interlocutory orders, including:

• High Court (Chancery Division) — the defendant obtained a partly successful extension-of-time application and the claimants obtained expedition: [2025] EWHC 1934 (Ch).
• High Court (Chancery Division) — the defendant’s anonymity application was unsuccessful: [2025] EWHC 1952 (Ch).