Can a witness use AI to prepare for cross-examination?
Artificial intelligence is often promoted as a tool for preparing for difficult conversations, interviews and presentations. It may therefore seem natural for a witness to ask an AI system what questions a barrister might put to them and how they should answer. In criminal proceedings, however, that can cross the line into prohibited witness coaching.
The Court of Appeal confronted the issue in R v FGD [2026] EWCA Crim 918. A complainant had used AI to work through possible cross-examination questions and suggested answers. The appeal court agreed that this amounted to coaching, but it also held that coaching does not automatically make a fair trial impossible.
What happened in R v FGD?
The case concerned an allegation of rape. The complainant, referred to as C, was the only prosecution witness. During cross-examination C was challenged about where they had been at a particular time on the night in question. After court, C searched cloud storage and produced screenshots intended to establish their location. When the prosecution sought to recall C, the defence asked for a full download of C's phone. The trial judge ordered the download.
The examination revealed two documents that contained a summary of C's recollection, followed by 24 detailed questions framed like cross-examination and suggested answers. The headings addressed central issues including what happened, consent and capacity, physical evidence and C's behaviour afterwards. It should be noted that although C asserted these were conversations with an AI that was not accepted by the defence who believed they were exchanges with a real person, presumably because the recovered documents contained no evidence of any prompts being given to the AI. The court did proceed on the basis that the conversation was with an AI though and so we will do the same.
The tone was significant. The AI said it would pull together everything C had shared so that C could see how “strong and consistent” the account was, and then work through the questions a defence lawyer might ask with suggested answers. This was not simply neutral information about what happens in court. It engaged directly with the evidence and how the witness might present it.
Witness familiarisation is permitted; coaching is not
The Court of Appeal applied the established distinction from R v Momodou and Limani [2005] EWCA Crim 177. A witness may be familiarised with the process of giving evidence. They can be told about the layout of the courtroom, the roles of the judge and advocates, how questioning works, the availability of special measures and the importance of listening carefully, asking for clarification and answering truthfully.
A witness can also refresh their memory from their own statement or recorded account in accordance with the normal rules. Lawyers may clarify practical matters and ensure that a witness understands what will happen. That support should reduce unnecessary anxiety without influencing the substance of the evidence.
Coaching is different. It involves rehearsing the evidence in the particular case, suggesting how questions should be answered, revealing what other witnesses have said so that accounts can be aligned, or encouraging a witness to change the content or emphasis of their account. The danger is not limited to deliberate dishonesty. An honest witness may unconsciously adapt their recollection to what appears to be a stronger, clearer or more acceptable answer.
An AI system can create the same danger. It may sound sympathetic, confident and authoritative while suggesting language or explanations that did not originate with the witness. The technology does not make the coaching permissible, and the fact that the witness acted without a lawyer's involvement does not remove its possible effect on the reliability of the evidence.
Why did the trial judge stop the case?
The defence applied to stay the prosecution as an abuse of process. It argued that no amount of cross-examination could establish which parts of C's evidence were genuinely C's and which had been influenced by the suggested answers. The Recorder agreed that the documents amounted to coaching and concluded that a fair trial was impossible.
The ruling brought the trial to an end. The prosecution appealed under section 58 of the Criminal Justice Act 2003, arguing that the Recorder had moved too quickly from finding coaching to assuming that a stay was the only possible remedy.
Why did the Court of Appeal reverse the judge’s decision?
A stay for abuse of process is an exceptional measure of last resort. Even serious difficulties for the defence should be managed through the trial if evidence, cross-examination, agreed facts and judicial directions can protect the defendant from unfairness.
Several features mattered. C's evidence-in-chief had been recorded in an Achieving Best Evidence interview years earlier, shortly after the incident and long before the use of AI. There were also contemporaneous messages to friends. That material had not been contaminated by the later preparation. The immediate concern was how the AI documents might have influenced C's answers in cross-examination.
The AI output was also preserved in writing. Traditional coaching can take place privately, leaving no reliable record of what was suggested. Here the documents could be disclosed to the parties, placed before the jury in full or summarised in agreed facts. C could be questioned about them, and the judge could give a firm direction explaining the risk that the evidence had been influenced.
Other options included an adjournment so the defence could investigate, discharging the jury and beginning again, an application to exclude C's evidence, or a submission that there was no case to answer once the prosecution evidence had been heard. The Court of Appeal did not decide in advance which measure had to be used. Its point was that the Recorder had not adequately considered the available ways of preserving a fair trial.
The prosecution appeal was allowed and the stay was reversed. That did not amount to a finding that C was truthful or that the defendant was guilty. Those were matters for a properly conducted retrial.
Does AI coaching always lead to a retrial or exclusion of evidence?
No automatic consequence follows from the label “coaching”. The response depends on the timing, content and extent of the interaction; whether the witness's earlier account remains available; whether prompts and outputs have been preserved; how central the affected evidence is; and whether the trial process can expose the problem fairly.
In an extreme case, evidence may be excluded or proceedings may be stayed. In another case, full disclosure, careful cross-examination and a tailored jury direction may be sufficient. The court must identify the actual prejudice and consider each possible remedy before taking the exceptional step of stopping a prosecution altogether.
AI use can widen disclosure enquiries
The Court of Appeal warned that a witness's use of AI may create new and potentially intrusive lines of enquiry. The prompts, the information supplied to the system, earlier versions of an account, the generated answers and any later changes may become relevant to reliability and credibility.
This does not give the defence an unrestricted right to search a complainant's phone or online life. In R v Bater-James [2020] EWCA Crim 790, the Court of Appeal stressed that examination of a digital device must follow a reasonable line of enquiry and remain proportionate. In FGD, the court itself expressed concern about the breadth of the order for a complete phone download, even though it happened to reveal highly relevant material.
The practical risk remains substantial. Once there is a proper basis for believing that AI may have shaped a witness's evidence, a focused investigation of the interaction may be justified when it would not otherwise have been necessary.
Practical guidance for witnesses
A witness who wants to understand the court process should speak to the solicitor who is dealing with the case in which they are involved. They should not ask an AI system to predict the questions in their case, improve their account, identify weaknesses, reconcile inconsistencies or draft suggested answers.
If AI has already been used, the safest course is to tell the legal representative promptly and preserve the complete interaction. Deleting selected messages or presenting only favourable extracts may create further difficulties. Early disclosure allows the legal team to assess whether the material is relevant, what must be preserved or disclosed and whether the court needs to give directions before evidence is resumed.
How Chetwode can help
Digital material can alter the fairness of a trial, but its significance depends on careful analysis of what was created, when it was created and how it may have affected the evidence. By contacting Chetwode Criminal Defence Solicitors we can identify the appropriate disclosure requests, preserve and examine relevant digital material, advise on expert evidence where required and make the application that properly reflects the prejudice in the individual case without opening you up to the risk of prosecution for misuse of artificial intelligence.
If you are a defendant or witness and AI has been used in connection with evidence, it is important to obtain advice before deleting, editing or circulating the material. A complete and accurate record gives the court the best chance of addressing the issue fairly.