The appellant, Felicity Harber, who was not represented at the tribunal, was disputing a failure to notify demand from HMRC for unpaid capital gains tax of £3,265.11 on a property sale but relied on fictitious case law produced using artificial intelligence (AI).

Harber provided the tribunal with the names, dates and summaries of nine FTT decisions in which the appellant had been successful in showing that a reasonable excuse existed.

However, none of those rulings were genuine; they had been generated by AI.

Harber said that she did not know the cases were ‘fabricated’ and had been generated by an AI system such as ChatGPT.

The tribunal quickly discovered that none of the cases were included in the FTT website or other legal websites like Bailii.

One of the AI generated fake cases was identified as ‘McMullen v HMRC (2018)’ in Harber’s deposition but the FTT could not find such a case. It identified a case involving the name McMullen but it related to a company called McMullen Holdings from 2011 [McMullen Holdings v HMRC [2011] UKFTT 327 (TC)] about a VAT penalty for late filing.

The AI case was clearly fabricated, referenced the wrong issue and the wrong year.  There were nine instances of fake cases, an excessive number of fake rulings to support the appellant.

While Harber lost her case as she did not have a reasonable excuse for failure to notify regardless of the fake cases, the judge said that ‘providing authorities which are not genuine and asking a court or tribunal to rely on them is a serious and important issue’.

Although the tribunal judge, Anne Redston, accepted that Harber did not know the AI cases were fake, she said: ‘We reject her submission that this did not matter because the tribunal had decided other reasonable excuse cases on the basis of ignorance of the law and/or mental health issues.’

The tribunal referenced the Mata v Avianca 22-cv-1461(PKC) case in the US where attorneys presented fake rulings to the Court.

‘We agree with Judge Kastel, who said on the first page of his judgment (where the term “opinion” is synonymous with “judgment”) that “many harms flow from the submission of fake opinions. The opposing party wastes time and money in exposing the deception… there is potential harm to the reputation of judges and courts whose names are falsely invoked as authors of the bogus opinions and to the reputation of a party attributed with fictional conduct”.’

The tribunal acknowledged that ‘providing fictitious cases in reasonable excuse tax appeals is likely to have less impact on the outcome than in many other types of litigation. But that does not mean that citing invented judgments is harmless’.

The case was dismissed.