Harber v The Commissioners for HMRC

What happened

Mrs Harber appealed penalties for failure to notify a liability to capital gains tax, arguing reasonable excuse on grounds of a mental health condition and ignorance of the law. In a written response she gave the Tribunal the names, dates and summaries of nine First-tier Tribunal decisions in which appellants had succeeded on reasonable excuse.

“However, none of those authorities were genuine; they had instead been generated by artificial intelligence.”

The Tribunal found as a fact that the cases “are not genuine FTT judgments but have been generated by an AI system such as ChatGPT”, and separately found as a fact that Mrs Harber was not aware they were fabricated and “did not know how to locate or check case law authorities by using the FTT website, BAILLI or other legal websites”.

The appeal was dismissed, applying the reasonable-excuse principles in Christine Perrin. The headnote records the finding plainly: “case law invented and not genuine”.

Why it belongs on this record

• EarliestJudgment date 4 December 2023, roughly eighteen months before Ayinde. It is the United Kingdom’s starting point.
• Not a lawyerA litigant in person, in a tax chamber. No professional duty was breached because no professional was involved.
• No sanctionAlongside Gamez and Warner v. Gilbarco, one of the decisions here where nothing was imposed. A record that only carries punishments is a campaign, not a record.
• The gap it exposesThe Tribunal’s finding that she did not know how to check a citation is the real subject of the case. The tools were available and free. She did not know they existed.

What it changed

It set the pattern every later UK decision followed: find whether the material is genuine, find whether the person knew, and separate those two questions completely. Harber is why Ayinde could distinguish between a barrister, a supervising solicitor and a blameless paralegal, and why Bandla could strike out an appeal without ever making a finding about AI.

It also explains a drafting choice that keeps recurring. Connecticut’s Practice Book section 4-9 binds “any person”. New South Wales’s Practice Note SC Gen 23 binds practitioners and unrepresented parties alike. New Zealand issued a set of AI guidelines specifically for non-lawyers. Every one of those choices anticipates a Mrs Harber.

Sources

• Decision, [2023] UKFTT 1007 (TC), Find Case Law, The National Archives, read in full
• Applied within: Christine Perrin v HMRC, on reasonable excuse

Related

• The full sanctions record
• Ayinde v Haringey
• Bandla v SRA
• Connecticut Practice Book section 4-9, which binds “any person”

Checked 5 August 2026 against the Tribunal’s own decision. No sanction was imposed on the appellant, and we say so.

Common questions

What was Harber v HMRC about?

An appeal against penalties for failure to notify liability to capital gains tax. The appellant argued she had a reasonable excuse because of a mental health condition and ignorance of the law, and supported it with nine First-tier Tribunal decisions. None of the nine were genuine. The Tribunal found as a fact that they had been generated by an AI system such as ChatGPT, and dismissed the appeal.

Was the appellant punished for citing fake cases?

No. The Tribunal accepted as a fact that she was not aware the cases were fabricated and did not know how to locate or check case law using the tribunal website, BAILII or other legal sources. The appeal was dismissed on its merits, not as a sanction for the citations.

Why does a 2023 tax tribunal case matter now?

Two reasons. It is the earliest United Kingdom instance on this record, roughly eighteen months before Ayinde. And it involved a litigant in person rather than a lawyer, which is the population most court AI rules now reach: Connecticut's Practice Book section 4-9 binds 'any person' who files, not only attorneys.

Do AI rules for courts apply to people without lawyers?

Increasingly yes. Connecticut's rule applies to any person who files. New South Wales Practice Note SC Gen 23 applies to legal practitioners and unrepresented parties alike. The Courts of New Zealand issued a separate set of AI guidelines specifically for non-lawyers.