A Witness's Own Use Of AI To Prepare For Cross-examination May Amount To Prohibited Witness Coaching

The Court of Appeal (Criminal Division) has made it clear that a witness's use of AI to prepare for cross-examination can amount to unlawful witness coaching: R v FGD [2026] EWCA Crim 918.

The only prosecution witness in a criminal trial used AI to produce a series of questions about their account together with suggested answers. At first instance, the court considered this to amount to witness coaching and stayed the proceedings as an abuse of process. 

Although the Court of Appeal overturned the stay on the basis that the prejudice caused could be addressed in other ways, it warned that coaching witnesses on their evidence by any means is not permitted. It emphasised that witnesses should be firmly discouraged from resorting to AI to prepare for giving evidence. Doing so could risk unfairness to the point where a court may have to consider excluding evidence. 

Although this is a criminal case, the same principles are likely to apply to civil proceedings, as witness coaching is equally forbidden in that context. Witnesses to any type of proceedings should be strongly advised not to use AI tools to prepare for giving evidence.

The use of AI in relation to witness statements is also receiving increasing attention. In particular, as part of its project to address the broader question of whether rules are needed to govern lawyers' use of AI  for the preparation of court documents, the Civil Justice Council is currently considering whether safeguards in relation to witness statements may be required. For more information, see our blog post here.

Background

The case concerned an allegation of rape. There was only one prosecution witness.

During cross-examination, the witness was challenged about their whereabouts on the night in question. They subsequently produced screenshots from their phone showing their location. When the prosecution applied to recall the witness and put the new material before the jury, defence counsel requested a full download of their phone. This was ordered by the Recorder. 

The download revealed two documents containing a summary of what the witness had recalled of the events on the relevant night and a series of questions in the form of a cross-examination of their account together with suggested answers (the AI documents). The witness confirmed that they had put material into AI to help prepare for court. 

Defence counsel applied to stay the proceedings, on the basis that a fair trial was impossible because no amount of cross-examination could adequately identify what evidence was properly the witness’s and what was somebody else’s. The Recorder was satisfied that the AI documents were evidence of coaching and stayed the proceedings as an abuse of process. 

The prosecution appealed on the basis that there were numerous other ways in which the prejudice occasioned could have been addressed. Prosecution counsel did not attempt to suggest that the AI documents did not amount to some form of forbidden witness coaching.

Decision 

The Court of Appeal (Lady Justice May, Mr Justice Griffiths and His Honour Judge Picton) allowed the appeal and reversed the stay, Lady Justice May giving the judgment. 

Witness training is forbidden. The dangers were succinctly summarised in R v Momodou and Limani [2005] EWCA Crim 177, in which the court noted that there is a dramatic distinction between impermissible witness training and permitted witness familiarisation. A witness should be able to give their evidence uninfluenced by what anyone else has said.

That said, the power to order a stay is an exceptional measure of last resort. It was not clear what steps the Recorder had considered when concluding that there could not be a fair trial. In particular, it was not clear why he had concluded that matters concerning the reliability and credibility of the witness's evidence could not safely be left to the jury, once they had been appraised of the nature and content of the AI documents and been given an appropriately robust direction. The witness’s evidence-in-chief, recorded some years before, would have been uncontaminated, leaving only their answers in cross-examination to be assessed against the coaching content of the AI documents. The trial process was well able to deal with potential prejudice to the defendant that arose from the use of AI. In addition, unlike traditional witness coaching which is conducted behind closed doors and not fully recorded, in this case everything that the AI “coach” had provided to the witness was fully recorded and could be placed before the jury in its entirety.

The Recorder had therefore erred in concluding that the defendant could not have a fair trial, or alternatively his decision to stay proceedings was not a reasonable decision for him to have made.

The court noted the growing use of AI for all manner of tasks, such as to answer everyday questions, apply for jobs, prepare for interviews and carry out research in many areas including the law. However, the coaching of witnesses on their evidence, by any means, is not permitted. All witnesses should be discouraged from resorting to the use of AI to prepare for giving evidence. This could run the risk of unfairness, to the point where the court might have to consider excluding evidence. 

The court observed that the Civil Justice Council had recently concluded a consultation on requirements for transparency regarding the use of AI in civil proceedings. It suggested that the National Police Chiefs Council, the Crown Prosecution Service and the Criminal Procedure Rules Committee might wish to consider how to address and regulate the use of AI in criminal proceedings, as this case is unlikely to be an isolated example.