Experts are advised, if possible, to avoid expressing opinions on the basis of possibility. The usually applicable stand of proof is the civil standard – the balance of probabilities or more probable than not. The criminal standard of proof is beyond reasonable doubt (and not beyond all reasonable [sic] doubt as it is sometimes misquoted). In this case it was submitted that the expert used the terms "possibility", "high possibility" and "extremely high possibility" interchangeably and that this was insufficient to satisfy the criminal standard of proof. However, when the court analysed the expert’s report as a whole, it was clear that a tribunal of fact could safely conclude that the criminal standard of proof was satisfied.
Government of Japan v Chappell [2025] EWHC 166