HMRC v. Gunnarson
Upper Tribunal (Tax and Chancery Chamber) · Jul 23, 2025
- Jurisdiction
- international
- Court
- Upper Tribunal (Tax and Chancery Chamber)
- Record ID
- hmrc-v-gunnarson-2025-07-23
- Observed outcome
- The UT allowed HMRC's appeal, set aside the FTT decision, and confirmed the assessment. Regarding the AI usage, the tribunal issued a formal warning to the respondent regarding the necessity of verifying AI-generated submissions.
- Known monetary consequence
- Not recorded
Why this matter warrants attention
The respondent, an unrepresented litigant, included three fictitious case citations in his skeleton argument after using generative AI for research. The Upper Tribunal identified the error following HMRC's verification, and the respondent subsequently removed the fabricated authorities. The tribunal issued a warning regarding the responsibility of litigants to verify AI-generated submissions.
The UT reasoned that while the respondent was not highly culpable as a lay litigant, the use of AI to generate fictitious citations is a serious matter. The tribunal highlighted that parties remain responsible for the accuracy of all submissions and that AI-generated content must be independently verified to prevent the introduction of misleading or fictitious information into court proceedings.
Opposing counsel will independently verify skeleton citations; expect HMRC-level scrutiny in any tax appeal.
Failure modes and consequences
- Hallucinated_case_law
- Pro Se
- Fake Citations
- Misrepresented Authority
- Tax
- Trial
- AI attribution
- Admitted
- Recorded tool
- Unidentified
- Known monetary consequence
- Not recorded
- Procedural posture
- Appeal to the Upper Tribunal (Tax and Chancery Chamber) from a First-tier Tribunal decision regarding the recovery of SEISS payments.
Damien Charlotin case archive
Publisher document archive. The recorded document is hosted in the upstream publisher archive.
Open underlying sourceA recorded source link is not a substitute for checking the underlying order, filing, opinion, or disciplinary record.
What this record does—and does not—establish
The respondent admitted to using online AI software but did not specify the tool.
The record summarizes the outcome described in the linked public source. The recorded document is hosted in the upstream publisher archive. This page is not a substitute for the complete docket, subsequent history, or jurisdiction-specific advice.
Latest evidence review: Primary Document Verified (high confidence).
Controls suggested by the public record
- Independently verify the existence and citation of every legal authority cited in submissions, regardless of the source.
- Inquire about the use of AI tools when opposing parties submit unusual or unverifiable authorities.
- Ensure that all legal research conducted via AI is cross-referenced against reliable, primary legal databases.