Harber v. HMRC

Outcome

Notes

AI UseCatherine Harber, a self-represented taxpayer appealing an HMRC penalty, submitted a document citing nine purported First-Tier Tribunal decisions supporting her position regarding "reasonable excuse". She stated the cases were provided by "a friend in a solicitor's office" and acknowledged they might have been generated by AI. ChatGPT was mentioned as a likely source.Hallucination DetailsThe nine cited FTT decisions (names, dates, summaries provided) were found to be non-existent after checks by the Tribunal and HMRC. While plausible, the fake summaries contained anomalies like American spellings and repeated phrases. Some cited cases resembled real ones, but those real cases actually went against the appellant.Ruling/SanctionThe Tribunal factually determined the cited cases were AI-generated hallucinations. It accepted Mrs. Harber was unaware they were fake and did not know how to verify them. Her appeal failed on its merits, unrelated to the AI issue. No sanctions were imposed on the litigant.Key Judicial ReasoningThe Tribunal emphasized that submitting invented judgments was not harmless, citing the waste of public resources (time and money for the Tribunal and HMRC). It explicitly endorsed the concerns raised in the US Mata decision regarding the various harms flowing from fake opinions. While lenient towards the self-represented litigant, the ruling implicitly warned that lawyers would likely face stricter consequences. This was the first reported UK decision finding AI-generated fake cases cited by a litigant