Artificial Intelligence Coaching of Witnesses

In the recent decision of R. v F.G.D [2026] EWCA Crim 918, 2026 WL 02081796, issues raised by the use of artificial intelligence to assist witnesses giving evidence was examined by the Court of Appeal Criminal Division.

At first instance, rape allegations were stayed by the trial judge during the evidence of the complainant (C). C was challenged during cross-examination about where C had been at a particular time on the evening in question. After court C went home and produced a series of screen shots to show where they had been, and when, that night. C’s telephone download contained a summary record of what C had recalled of events on the night in question, followed by a series of questions in the form of a cross-examination of C's account, together with suggested answers amounting to a  documentary record of witness-coaching. C was asked who they had been communicating with, to which C responded: "I had put stuff into AI to help me prepare myself for the court".

The trial Judge stayed proceedings as abuse of process, citing Momodou [2005] EWCA Crim 177, in which it is clear that witness training for criminal trials is prohibited.

In R. v F.G.D the Court of Appeal allowed the prosecution’s section 58 CJA appeal, as the trial Judge had erred as a matter of law.

May, LJ observed [20]: "... we are satisfied that the Recorder erred in concluding that R could not have a fair trial, alternatively that his decision to stay proceedings was not a reasonable decision for him to have made. We can understand why the Recorder fell into this error, given the apparent concession which he understood prosecuting counsel to have made; in future we would encourage counsel on both sides when dealing with an application to stay for abuse explicitly to raise and explore all the ways in which the trial process could deal with any potential prejudice so that the trial judge is able to consider and deal with each separately, when ruling on the issue..."

Continuing [23]:

"... The coaching of witnesses in their evidence, by any means, is not permitted. All witnesses, whether for the prosecution or defence, should be firmly discouraged from resorting to the use of AI to prepare for giving evidence. Doing so could run the risk of unfairness up to the point, in an extreme case, where the court may have to consider excluding evidence. Moreover, for complainants in cases involving allegations of sexual misconduct, their use of AI may open up further lines of enquiry, exposing their online activity to an unwelcome, wider-ranging and potentially more intrusive investigation and examination for the purposes of disclosure, than would otherwise have been required. Using AI may also put their personal information into the public domain, in open AI, in a way that they may never have anticipated."

The court went on to say [24] “… that, to the extent that they are not already doing so, the National Police Chiefs Council, the Crown Prosecution Service and the Criminal Procedure Rules Committee may wish to consider how to address and regulate the use of AI in criminal proceedings. This case is unlikely to be an isolated example”.

On the facts of FGD, the AI "coach" provided to C was fully recorded and could be placed in its entirety before the jury, or summarised by agreement and put into agreed facts, to ensure a fair trial.

In the earlier case of Momodou, the Court of Appeal warned of the danger of the coaching of witnesses. In Momodou the prosecution arose from a Violent Disorder at Yarl’s Wood Immigration Detention Centre in Bedfordshire in 2002. The centre was run by detention custody officers (DCO) employed by Group 4. The DCO witnesses received trauma debriefings (run by the Independent Counselling and Advisory Service (ICAS)) as they had witnessed the disorder and received advice from commercial solicitors who represented Group 4, in a linked civil claim by the police against Group 4. Witness training was arranged by Group 4 for the DCOs, the inference being that Group 4 was concerned to protect its position in the civil proceedings.

Once prosecution counsel became aware of the training proposals, he advised that it was wrong in criminal proceedings, and might constitute a contempt of court both by Group 4 and the training company. The training programme was stopped immediately. However, sixteen potential witness for the prosecution had received training.

It was an agreed fact between the prosecution and defence at trial that the training offered was ‘wholly inappropriate and improper’. The trial judge expressly agreed and directed the jury that ‘there is no place for witness training in our country, we do not do it. It is unlawful’. In the case of one defendant, against whom the evidence largely consisted of witnesses who had been trained, he withdrew the case from the jury.

In relation to witness training and coaching Judge LJ made the following observations:

[61] "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 witness should give his or her own evidence, so far as practicable uninfluenced by what anyone else has said, whether in formal discussions or informal conversations. The rule reduces, indeed hopefully avoids any possibility, that one witness may tailor his evidence in the light of what anyone else said, and equally, avoids any unfounded perception that he may have done so. These risks are inherent in witness training. Even if the training takes place one-to-one with someone completely remote from the facts of the case itself, the witness may come, even unconsciously, to appreciate which aspects of his evidence are perhaps not quite consistent with what others are saying, or indeed not quite what is required of him. A honest witness may alter the emphasis of his evidence to accommodate what he thinks may be a different, more accurate, or simply better remembered perception of events. A dishonest witness will very rapidly calculate how his testimony may be ‘improved’. These dangers are present in one-to-one witness training. Where however the witness is jointly trained with other witnesses to the same events, the dangers dramatically increase. Recollections change. Memories are contaminated. Witnesses may bring their respective accounts into what they believe to be better alignment with others. They may be encouraged to do so, consciously or unconsciously. They may collude deliberately. They may be inadvertently contaminated. Whether deliberately or inadvertently, the evidence may no longer be their own. Although none of this is inevitable, the risk that training or coaching may adversely affect the accuracy of the evidence of the individual witness is constant. So we repeat, witness training for criminal trials is prohibited."