ICAEW's Tax School explains why the Superior Court decision, taken over on July 23, 2025, will take a timely reminder of the need to verify the accuracy of AI responses on tax issues.
At HMRC v Marc Gunnarsson [2025] UKUT 00247 (TCC), Upper Court (UT), agreed to the HMRC that it is correct to collect the coronavirus assistance payments made to Gunnarsson under the Self-Employment Income Support Scheme. Gunnarson was a “unrepresented litigator” and means he represented himself before UT.
Gunnarsson sent a draft of the skeleton discussion to HMRC prior to the hearing. This referred to three decisions made by the First Level Court (FTT) that he said he supported his case. Notified by HMRC that no decision was present, Gunnarsson sent out a revised final skeleton discussion that did not mention the decision. During the hearing, Gunnerson accepted that he used AI to help him submit his written submission.
When commenting on Gunnarsson's use of AI, UT refers to the case of Ayinde. [2025] EWHC 1383 (Admin). This captures the dim views of lawyers who did not check written legal arguments prepared by the departmental courts by AI. In its decision, the divisional court sets out the current regulatory framework for lawyers and calls for more to be done to “deal with the misuse of artificial intelligence.”
UT makes it clear that legal representatives and unrepresented litigators are responsible for “both reliability and reliability, the accuracy of information, both evidence and submission, and presenting it to FTT or UT.” The decision concludes with a warning that UT may consider making the issue “very serious” and impose sanctions on parties or representatives found to have misused AI.
Thanks to Gunnarsson, UT did not feel he was “very responsible” as he was not properly trained or qualified. However, parties to future tax agreements may not be treated generously.
This is not the first case involving AI responses referring to fictional sources. Other examples include the FTT decision for Felicity Harbor v HMRC [2023] UKFTT 1007 (TC) and Bodrul Zzaman V HMRC [2025] UKFTT 539 (TC).
ICAEW publishes a wide range of AI guidance and resources, including how to manage the risks of using AI.
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