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HMRC v. Gunnarson

Court
Upper Tribunal (Tax and Chancery Chamber)
Jurisdiction
UK
Decided
2025-07-23
AI tool
Unidentified
Outcome
Warning
Monetary penalty
None reported

What was hallucinated

Fabricated: Case Law | Respondent’s skeleton cited a non-existent FTT authority said to show HMRC’s SEISS guidance was unclear; UT records HMRC checked and the case does not exist. || Fabricated: Case Law | Respondent’s skeleton cited a non-existent FTT decision claiming reliance on accountant’s advice and guidance was relevant; UT notes HMRC verified the case does not exist. || Fabricated: Case Law | Respondent’s skeleton cited a non-existent FTT decision asserting a purposive approach allowed SEISS based on continuity of work; UT records the citation is fictitious. || Misrepresented: Legal Norm | FTT applied an ‘honest belief’ eligibility test not found in the SEISS Directions or FA 2020; UT held this was a legal error.

Sanction teardown · Upper Tribunal (Tax and Chancery Chamber), UK · 2025-07-23

HMRC v. Gunnarson

What happened

In Upper Tribunal (Tax and Chancery Chamber), UK, a filing relied on an unnamed/unconfirmed AI tool to help draft legal argument. The court identified the following problems with the citations in that filing:

  • Fabricated (Case Law)
    Respondent’s skeleton cited a non-existent FTT authority said to show HMRC’s SEISS guidance was unclear; UT records HMRC checked and the case does not exist.
  • Fabricated (Case Law)
    Respondent’s skeleton cited a non-existent FTT decision claiming reliance on accountant’s advice and guidance was relevant; UT notes HMRC verified the case does not exist.
  • Fabricated (Case Law)
    Respondent’s skeleton cited a non-existent FTT decision asserting a purposive approach allowed SEISS based on continuity of work; UT records the citation is fictitious.
  • Misrepresented (Legal Norm)
    FTT applied an ‘honest belief’ eligibility test not found in the SEISS Directions or FA 2020; UT held this was a legal error.

Which AI tool

an unnamed/unconfirmed AI tool. Note: Charlotin's public database records tool attribution only where a court order, brief, or reporting on the matter states it explicitly; "unidentified" or "implied" means the record indicates AI use but does not name a specific product — we do not guess.

Outcome

Warning

How Citation Safe would have caught this

Citation Safe runs three deterministic layers before a brief is filed: (1) does the citation exist against CourtListener's database of published opinions, (2) if quoted, does that exact language appear in the source, (3) does the cited case actually support the proposition it is cited for. Fabricated case citations fail Layer 1. Fabricated or misattributed quotations fail Layer 2 even when the underlying case is real. Misrepresented holdings — a real case cited for a proposition it does not support — are the target of Layer 3. None of these checks involve asking another language model whether the citation looks right; they are lookups and text-matches against the actual source, which is why a hallucinated citation has to survive a direct lookup against the authoritative source — not another model's opinion — to earn a VERIFIED stamp; our measured false-verify rate is published live at /quality.

Check a brief before you file it → · See our live false-verify rate

Source: https://www.damiencharlotin.com/documents/644/HMRC_v._Gunnarson_UK_23_July_2025.pdf, via Damien Charlotin's public AI Hallucination Cases Database (CC0).

Source: https://www.damiencharlotin.com/documents/644/HMRC_v._Gunnarson_UK_23_July_2025.pdf

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