Invalid AI-Generated Legal Precedents Dismissed by Tribunal in Tax Law Case

Citation: [2023] UKFTT 1007 (TC)
Judgment on


In the case of Felicity Harber v The Commissioners for HMRC, the First-tier Tribunal (Tax Chamber) evaluated an appeal against a penalty for failure to notify liability for Capital Gains Tax (CGT). The Appellant, Mrs. Harber, argued that she had a reasonable excuse based on her mental health condition and ignorance of the law. The case examines the validity of AI-generated case law as authorities in legal proceedings, principles of reasonable excuse under tax law, and the obligations of the taxpayer in notifying tax liabilities.

Key Facts

Mrs. Harber disposed of a property, incurring a CGT liability which she failed to notify to HMRC. HMRC issued a penalty, which Mrs. Harber appealed, providing AI-generated cases as precedent and citing her mental health and ignorance of the law as reasonable excuses. The Tribunal had to determine the authenticity of the AI-generated cases and whether Mrs. Harber had a reasonable excuse for her failure to notify.

Several legal principles crucial to tax law disputes were applied:

Artificial Intelligence-Generated Case Law

The Tribunal clarified that the AI-generated cases provided by Mrs. Harber were not valid legal authorities. Important legal references include the US case of Mata v Avianca 22-cv-1461(PKC), dealing with submissions of fake AI-generated opinions. Utilizing fictional cases undermines the judicial process and constitutes an inappropriate use of artificial intelligence in legal proceedings.

Reasonable Excuse Under Tax Law

The principal case cited for defining “reasonable excuse” is Christine Perrin v HMRC [2018] UKUT 156. The Upper Tribunal in Perrin provided a structured analytical process for evaluating reasonable excuses and emphasized that ignorance of the law might constitute a reasonable excuse depending on the circumstances.

In assessing Mrs. Harber’s claim to a reasonable excuse, the Tribunal applied the principles from Perrin, considering the taxpayer’s experience, capabilities, and external factors in determining whether her ignorance of the law or mental health issues could be deemed objectively reasonable.

Taxpayer’s Obligation to Notify

Under Section 7 of the Taxes Management Act 1970, taxpayers who are chargeable to income tax or capital gains tax are obligated to notify HMRC within a specified timeframe if they have not received a notice to file a tax return. The Tribunal examined whether Mrs. Harber adhered to her obligation to notify HMRC of her CGT liability within the relevant notification period.


The First-tier Tribunal dismissed Mrs. Harber’s appeal for the following reasons:

  1. The AI-generated cases were not genuine and recognized by the Tribunal as invalid.
  2. Mrs. Harber’s mental health condition did not constitute a reasonable excuse because it did not impede her ability to notify HMRC of her CGT liability.
  3. Mrs. Harber’s ignorance of the law was not considered objectively reasonable as she was aware of her tax obligations and had not sought advice in a timely manner.

Consequently, the Tribunal confirmed the penalty imposed by HMRC for the failure to notify liability.


The Felicity Harber v The Commissioners for HMRC case reaffirms that the validity and genuineness of case law are paramount in legal proceedings. The pivotal role of reasonable excuse in tax law disputes is further underlined, particularly the requirement that ignorance of the law can only be considered a reasonable excuse when it is objectively reasonable for the taxpayer in their particular circumstances. The case illustrates the Tribunal’s application of established principles to contemporary issues, such as the use of AI-generated information in court proceedings. This decision serves as an important reminder for taxpayers of their obligation to be proactive in understanding and complying with their tax liabilities.