In a stern intervention, a judge at the High Court of England and Wales issued a formal warning to legal professionals on Friday, declaring that lawyers who submit fictitious cases generated by artificial intelligence could face criminal charges.

The senior judge scolded lawyers in two cases who apparently used AI tools when preparing written arguments that were presented in court.

“There are serious implications for the administration of justice and public confidence in the justice system if artificial intelligence is misused,” Victoria Sharp, president of the King’s Bench Division of the High Court, said in the judgment delivered on Friday.

In the judgment, Sharp also referred to “concerns about the competence and conduct of the individual lawyers who have been referred to this court,” and concluded that all previous guidance seems to be “insufficient to address the misuse of artificial intelligence.”

The lawyer denied using AI but admitted that she might have inadvertently done so while researching on the internet in preparation for her case.

The ruling comes after so-called hallucinations — AI-generated fictions — have cropped up at big law firms since AI programs such as ChatGPT have become widely available.