The Court of Appeal has delivered an important judgment on the use of artificial intelligence (AI) by witnesses. This confirmed that a witness's own use of AI to prepare for giving evidence can amount to prohibited witness coaching.
In R v FGD [2026] EWCA Crim 918, the Court considered the consequences of a prosecution witness using AI to generate a series of questions challenging their account, together with suggested responses. While the Court ultimately overturned a stay of proceedings that had been granted at first instance, it issued a clear warning that witnesses should not use AI tools to prepare the substance of their evidence.
The judgment is one of the clearest judicial statements to date on the risks associated with AI-assisted witness preparation and is likely to be of interest to litigators, in-house counsel and anyone involved in dispute resolution.
The facts of R v FGD
The case arose in the context of a criminal trial involving a single prosecution witness. During the proceedings, material recovered from the witness's phone revealed documents generated with the assistance of AI.
These documents included:
- A summary of the witness's recollection of events.
- A series of questions framed in the style of cross-examination.
- Suggested answers for responding to those questions.
The witness confirmed that they had used AI to help prepare for giving evidence in court.
Defence counsel argued that this undermined the integrity of the witness's evidence to such an extent that a fair trial was no longer possible. Specifically, it was said that the jury would be unable to distinguish between the witness's genuine recollection and responses influenced by AI-generated content.
Why the trial was stayed
At first instance, the trial judge concluded that the AI-generated material amounted to witness coaching and stayed the proceedings as an abuse of process.
The concern was that the witness's evidence may have been contaminated by an external source. This compromised the fundamental principle that witnesses should give evidence based on their own recollection rather than a rehearsed or manufactured account.
The decision reflected a long-established distinction in English law between legitimate witness familiarisation and prohibited witness coaching.
The Court of Appeal’s decision
The Court of Appeal overturned the stay and held that the prejudice caused by the AI-generated material could be addressed through the ordinary trial process, including disclosure, cross-examination and judicial directions.
However, the Court left no doubt about its view of the underlying conduct.
Lady Justice May reaffirmed the principle established by Judge LJ in R v Momodou and Limani [2005] EWCA Crim 177: “There is a dramatic distinction between witness training or coaching, and witness familiarisation. Training or coaching for witnesses in criminal proceedings (whether for prosecution or defence) is not permitted.”
The Court emphasised that the prohibition on witness coaching applies regardless of the method used. The fact that the coaching was generated by an AI system rather than another individual did not alter the underlying concern.
AI and witness preparation: The Court’s warning
A notable aspect of the judgment is the Court's recognition that AI tools are increasingly being used for everyday tasks, including research, interview preparation and legal inquiries.
Nevertheless, Lady Justice May stressed that witnesses should be “firmly discouraged” from using AI to prepare for giving evidence. The Court warned that such conduct could result in unfairness and, in extreme circumstances, might justify the exclusion of evidence altogether.
The judgment highlights several key risks:
- AI-generated content may influence or reshape a witness's recollection.
- It may become difficult to determine what evidence is genuinely the witness's own.
- The use of AI could generate additional disclosure issues.
- Wider examination of a witness's digital activity may become necessary.
- Personal information entered into AI systems may be stored or processed in ways not anticipated by the user.
Potential implications for civil litigation
Although R v FGD was decided in the criminal context, the underlying principles are unlikely to be confined to criminal proceedings.
Witness coaching is equally impermissible in civil litigation and courts are likely to apply similar reasoning where a witness uses AI to rehearse answers or refine their evidence before trial.
The decision also comes at a time when the legal profession is grappling with the broader implications of AI. The Civil Justice Council is currently considering issues relating to the use of AI in the preparation of court documents, including potential safeguards relating to witness evidence and statements.
As AI tools become more sophisticated and accessible, courts can be expected to scrutinise more closely how they are being used within the litigation process.
Practical guidance for witnesses and legal teams
The key message from R v FGD is that witnesses should not use AI to prepare the substance of their evidence. This is of course to be differentiated from emotion AI on a neutral topic during the witness familiarisation process.
Legal representatives should ensure that witnesses understand:
- The distinction between familiarisation and coaching.
- That AI-generated mock cross-examinations and suggested answers create significant risks.
- That digital records of AI interactions may become disclosable.
- That improper use of AI could undermine the credibility of evidence and affect the outcome of proceedings.
Conclusion
The Court of Appeal's decision in R v FGD represents a landmark moment in the developing relationship between artificial intelligence and litigation. While the Court stopped short of finding that AI-assisted witness preparation automatically renders a trial unfair, it made clear that using AI to rehearse evidence can amount to prohibited witness coaching.
As AI becomes increasingly embedded in professional and personal life, litigants, witnesses and legal advisers must ensure that its use does not compromise the core principle that witness evidence should be the witness's own. The message from the Court is clear: when preparing to give evidence, AI is not a substitute for authentic recollection.
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