Pinsent Masons reprimanded by High Court over AI-generated false citations

TL;DR:

• London’s High Court has admonished top-20 UK firm Pinsent Masons after a junior lawyer twice misled the court by citing a statute fabricated by an AI tool, in a routine insolvency application.
• Judge Mark Mullen ruled that work pressure did not excuse failure to verify, warning that legal professionals “cannot outsource the process of legal research or of legal reasoning to an AI”.
• Pinsent Masons has apologised and self-referred to the Solicitors Regulation Authority; the firm was already piloting a new AI tool when the error occurred.

The reprimand puts a second top-tier UK law firm in front of the SRA this year over generative-AI misuse, and lands less than a fortnight after the IOPC reported that around a quarter of judicial review requests now appear to be AI-drafted — some citing invented English statutes.

Context and Background

The submissions in question came from a junior lawyer with oversight from a senior associate and a partner, neither of whom said they knew AI was being used. The transcript filed by the firm included an explicit warning from the AI bot that it was “not fully confident” of the statutory wording and advising verification — which did not happen. Pinsent Masons’ equity partners were paid an average of £797,000 last year, a figure Mullen’s judgment did not reference but which sharpens the workload-versus-quality argument the court was making.

This is the third public reprimand of UK barristers or solicitors over AI hallucinations in roughly a year. The High Court handed down a 2024 judgment over two separate cases involving suspected AI-fabricated material — one with 18 false citations. Earlier this month, US firm Sullivan & Cromwell told a federal bankruptcy court its filing contained multiple AI hallucinations. The pattern looks structural rather than incidental: as the Resultsense analysis of the Ayinde judgment noted yesterday, the Civil Procedure Rules were built around human accountability and sit awkwardly with probabilistic systems.

Mullen declined to initiate contempt proceedings, citing the firm’s self-referral and absorption of client costs — a relatively light landing, but one that signals the senior judiciary is escalating commentary rather than sanctions. The SRA confirmed it is “looking into” the report before deciding next steps.

Looking Forward

For UK law firms, the practical question is no longer whether to allow AI in research workflows but how to document supervision and verification. Pinsent Masons told the court it has added safeguards around the new tool; expect peer firms to formalise pre-submission AI-disclosure protocols rather than waiting for the SRA or the Bar Standards Board to mandate them. The IOPC data and this week’s High Court ruling will give that internal-governance argument considerable institutional weight.