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Incident Tracker / United Kingdom

HMRC v Gunnarsson, [2025] UKUT 247 (TCC)

·Upper Tribunal (Tax and Chancery Chamber)·UKDismissal

Before the Upper Tribunal (Tax and Chancery Chamber), unrepresented respondent Marc Gunnarsson cited three non-existent First-tier Tribunal decisions produced by online AI software. The Upper Tribunal set aside the FTT decision, dismissed his appeal and confirmed recovery of £12,918 in wrongly claimed grants, warning that AI chatbots frequently mislead litigants in person.

Court
Upper Tribunal (Tax and Chancery Chamber)
Date
2025-07-23
Who used the AI
Not recorded
AI tool
Not identified in the record
Conduct
An unrepresented respondent cited three non-existent First-tier Tribunal decisions (Patel, Ali and Kamran v HMRC) in his skeleton argument. He acknowledged using online AI software to prepare his submissions; the fabricated authorities were removed in an amended skeleton the same day.
Outcome
Dismissal
Penalty
No monetary penalty recorded
Regulatory outcome
No separate regulatory disposition recorded
Status
Verified against listed sources
Last checked
2026-09-11

What was fabricated or misused

  • Patel v HMRC [2023] UKFTT 138 (TC) — the case did not exist
  • Ali v HMRC [2022] UKFTT 329 (TC) — the case did not exist
  • Kamran v HMRC [2023] UKFTT 91 (TC) — the case did not exist

What the court said

“This contained reference to three previous decisions purportedly made by the FTT which were said to support the Respondent’s interpretation of the legislation.”
Upper Tribunal (Tax and Chancery Chamber), [107]
“They discovered that the cases referred to by the Respondent do not exist.”
Upper Tribunal (Tax and Chancery Chamber), [108]
“The accuracy of Artificial Intelligence (AI) should not be relied upon without checking, particularly when it comes to statements or arguments that it makes concerning the law.”
Upper Tribunal (Tax and Chancery Chamber), [112]
“On these facts, we do not consider the Respondent to be highly culpable because he is not legally trained or qualified, not subject to the same duties as a regulated lawyer or other professional representative and may not have understood that the information and submissions presented were not simply unreliable but fictitious.”
Upper Tribunal (Tax and Chancery Chamber), [114]

Timeline

  1. HMRC issued the assessment later challenged in the FTT.
  2. FTT allowed Gunnarsson's appeal in part.
  3. UT emailed plain-language skeleton guidance after no skeleton was filed.
  4. Gunnarsson filed a first draft skeleton citing three purported FTT decisions.
  5. UT heard the appeal; Gunnarsson accepted he used online AI software.
  6. UT judgment allowed HMRC's appeal and addressed the AI citations.

Why this case matters

Gunnarsson is a UK litigant-in-person counterpart to Ayinde. The Upper Tribunal repeated the same verification duty but applied it with a different response because the respondent was unrepresented, under time pressure, and not legally trained. It still made the taxpayer responsible for the accuracy of submissions and recorded the burden placed on HMRC. The record helps separate two policy questions: how courts should warn and manage self-represented AI use, and when misuse becomes sanctionable conduct.

Practice note

A self-represented party using AI for a skeleton argument should verify every case in Find Case Law, BAILII, tribunal databases, or the official source before filing. If the case cannot be found, remove it. The same check must cover the holding: a real decision is not usable unless it says what the submission claims.

Primary sources for this incident

Related regulation records for this incident

No related regulation record has been linked to this incident yet.

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Cite this record

SafeLegalAI Global Legal AI Incident Tracker, “HMRC v Gunnarsson, [2025] UKUT 247 (TCC)”, safelegalai.com/tracker/hmrc-v-gunnarsson (accessed 2026-09-16). Data: CC BY 4.0.

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