TL;DR

A rape trial at Lewes Crown Court was halted after the complainant admitted preparing for cross-examination with an AI chatbot. Chat logs recovered from her phone showed headings including “On Consent and Capacity” and “On Physical Evidence”. In R v FGD [2026] EWCA Crim 918 the Court of Appeal held that using AI this way amounts to witness coaching, which is prohibited — while reversing the stay and ordering a retrial.

The chatbot had offered to let the witness “see how strong and consistent your account actually is” and to work through “every question a defence lawyer might ask with suggested answers”. Defence counsel argued no amount of cross-examination could then separate the witness’s own recollection from the machine’s. The Recorder agreed and stayed proceedings; the Court of Appeal found the trial process could handle the prejudice and remitted the case.

On the principle the court was unequivocal. Witnesses should be “firmly discouraged from resorting to the use of AI to prepare for giving evidence.” Its reasoning follows R v Momodou [2005] EWCA Crim 177: an honest witness may unconsciously shift emphasis to match a better-remembered account, while a dishonest one “will very rapidly calculate how his testimony may be ‘improved’.”

Analysis published by Slaughter and May stresses the reach beyond criminal work. The familiarisation-versus-coaching line — court layout and the experience of giving evidence are fine, rehearsing substance is not — applies in civil proceedings too, and Bar Council guidance already bars coaching clients on the “right” answer. The firm notes the ruling matters to civil practitioners and to witnesses in both jurisdictions.

The exposure here is unusual: the logs only surfaced because the complainant volunteered screenshots after cross-examination, which put her phone contents into the defence’s hands. Absent that, nobody would have known.

Looking Forward

The practical consequence is a disclosure problem nobody has solved. Chatbot use leaves a record on a device, and a witness who prepared with AI now carries potentially disclosable material into court. Solicitors preparing witness statements will need to ask the question directly, and add it to standard client instructions — because the alternative is finding out mid-trial, as happened at Lewes.