AI as witness coach? Court of Appeal draws the line

Can a witness who turns to AI for assistance in preparing for cross-examination be said to have been impermissibly “coached”? In R v FGD [2026] EWCA Crim 918, the Court of Appeal (Criminal Division) has answered that question in the affirmative.

It was found that, in preparation for a criminal trial, a witness for the prosecution had fed material into an AI tool to generate a summary of their factual recollection, along with a list of likely cross-examination questions and suggested answers. The AI tool explained that this would let the witness “see how strong and consistent [their] account actually is” and that it would “go through every question a defence lawyer might ask with suggested answers”. Defence counsel applied to stay the proceedings on the basis that no amount of cross-examination could adequately identify what evidence was properly the witness’s own and what had originated from the AI tool. The Recorder agreed that it would be impossible for the defendant to have a fair trial on that basis.   

While the Recorder treated this as coaching and stayed the proceedings, the Court of Appeal reversed the stay, finding on the facts that the trial process could adequately address any prejudice caused by the coaching. The case was accordingly remitted for re-trial. The Court of Appeal was nonetheless unequivocal on the underlying principle: coaching witnesses on the substance of their evidence, by whatever means, including through the use of AI, is prohibited. The Court further noted that witnesses should be “firmly discouraged” from using AI to prepare for giving evidence at trial. 

The Court of Appeal’s decision referred to the rationale given by the leading authority in this area, R v Momodou [2005] EWCA Crim 177, which confirmed that coaching risks a witness’s evidence no longer being their own. For example, an honest witness may unconsciously alter the emphasis of their evidence to accommodate what they believe to be a more accurate or better remembered account of events, while a dishonest witness may deliberately recalibrate their testimony to improve it. That authority drew a clear distinction between familiarisation (such as with the court layout and the general experience of giving evidence), which is permissible, and coaching, which is not, since the latter risks that evidence ceasing to be the witness’s own uninfluenced account. 

Although the Court of Appeal’s consideration of this issue in both R v FGD and R v Momodou arose in the context of criminal cases, it is firmly established that witness training (as opposed to witness familiarisation) is also prohibited in civil proceedings. Bar Council guidance, for example, makes clear that rehearsing questions with the client, and/or coaching the client on the “right” answer to be given or how to express themselves on any question or issue, is impermissible. As such, this case is of note not just to criminal, but also to civil practitioners, and to witnesses in both criminal and civil proceedings.