Think Before You Prompt: The Risks of AI-Assisted Witness Preparation

The Court of Appeal has delivered one of the first appellate decisions in England and Wales to consider the use of generative AI by a witness preparing to give evidence. In R v FGD [2026] EWCA Crim 918, he Court ultimately reinstated a prosecution that had been stayed at first instance and provided an important warning about the risks of AI assisted witness preparation.

How did the issue arise?

The case concerned a rape allegation in which the complainant was the sole prosecution witness. During cross-examination, the complainant was challenged about their whereabouts at a particular time on the relevant evening. After court that evening, the complainant searched their cloud storage and located screenshots which they believed confirmed their location. When the prosecution sought to rely on that material, the defence requested a download of the complainant's phone. The Court noted there appeared already to have been concerns regarding disclosure of relevant phone material. The trial was adjourned while the download was carried out.

The download revealed two documents generated through the complainant's interaction with AI. The documents contained a summary of the complainant's account of events together with a series of potential cross-examination questions and suggested answers. One passage informed the complainant that the AI would show them "how strong and consistent your account actually is" before going through "every question a defence lawyer might ask with suggested answers".

The Recorder's decision

The Recorder concluded that the material amounted to witness coaching and stayed the proceedings as an abuse of process. The concern was that it was no longer possible to know what aspects of the complainant's evidence reflected their genuine recollection and what aspects may have been influenced by the AI-generated material.

The Court of Appeal's judgment

The Court of Appeal reaffirmed the long-established principle that witness coaching is prohibited. Relying on R v Momodou and Limani [2005] EWCA Crim 177, it reiterated that witnesses should give their own evidence, uninfluenced by suggestions from others, and that coaching risks contaminating recollection and undermining confidence in the integrity of the evidence.

However, the Court held that the Recorder had gone too far in concluding that a fair trial was impossible. A stay is an exceptional remedy of last resort and should only be ordered where the ordinary processes of a trial cannot adequately address the relevant prejudice.

In this case, the AI material had been identified and preserved. The jury could therefore have been told about its contents, the complainant could have been cross-examined about it, and the judge could have directed the jury on how to approach any reliability concerns. The Court considered this to be precisely the type of issue that the trial process is designed to manage.

Why is the decision significant?

The judgment is significant because it demonstrates that courts are now confronting the practical consequences of widespread AI use.

The Court stopped well short of suggesting that any use of AI by a witness will automatically render evidence inadmissible or a trial unfair. Nevertheless, it delivered a clear warning:

"All witnesses, whether for the prosecution or defence, should be firmly discouraged from resorting to the use of AI to prepare for giving evidence." ([23])

The Court further warned that AI-assisted witness preparation may create risks of unfairness and, in an appropriate case, could justify the exclusion of evidence.

The decision also highlights a potentially overlooked consequence of AI use. The complainant's interactions with AI became discoverable because they were stored on their device and uncovered during disclosure. The Court observed that the use of AI may generate additional lines of enquiry, expose online activity to greater scrutiny and result in personal information being uploaded to AI platforms in ways that users may not fully appreciate.

Looking ahead

The Court recognised that this case is unlikely to be an isolated example and suggested that the Crown Prosecution Service, the National Police Chiefs' Council and the Criminal Procedure Rules Committee may wish to consider how the use of AI should be addressed in criminal proceedings.

As AI becomes increasingly embedded in everyday life, R v FGD is likely to be viewed as an early and important authority on the interaction between AI, and witness evidence. The message from the Court is clear: while AI may assist with many aspects of daily life, it should not be used to shape, rehearse or refine witness evidence that must ultimately remain the witness's own.