Expert Witness in Lucy Letby Trial Hid Hospital Investigation

Published: 11 March 2026 The English Chronicle Desk The English Chronicle Online – UK News

The integrity of expert testimony in one of the most scrutinised criminal cases in recent British history has come under renewed pressure after it emerged that a key prosecution witness in the Lucy Letby trial did not disclose that he was under formal investigation by his own hospital at the time he gave evidence. Both Cheshire police and the Crown Prosecution Service (CPS) have confirmed they were unaware of the inquiry into the medical conduct of Prof Peter Hindmarsh before he appeared in court to support the prosecution’s case that Letby had attempted to murder two infants by injecting insulin into their fluid bags.

The revelation adds a new layer of complexity to a case already mired in controversy, with Letby’s legal team and a growing number of medical experts arguing that the convictions may be unsafe. The Guardian’s investigation last week uncovered that University College London Hospitals NHS Trust (UCLH), Hindmarsh’s primary employer, had launched a formal investigation into multiple serious concerns about his clinical practice. Great Ormond Street Hospital, where he also held an honorary consultancy, was involved in the inquiry. The allegations were wide‑ranging and included claims that Hindmarsh had harmed patients. These concerns were being actively examined in the months leading up to the Letby trial.

Under the rules governing criminal proceedings, expert witnesses are required to disclose anything that could reasonably be seen as undermining their credibility, impartiality, or the reliability of their professional opinion. Senior legal figures have told the Guardian that this duty extends to internal investigations by an expert’s employer, particularly when the allegations relate directly to competence or conduct. In Hindmarsh’s case, the investigation was not disclosed to Cheshire police before he took the stand on 25 November 2022.

Hindmarsh’s evidence was central to the prosecution’s argument in two of the most pivotal charges against Letby: the alleged insulin poisonings of babies known as F and L. These were among the few counts on which the jury returned unanimous guilty verdicts. The prosecution relied heavily on Hindmarsh’s interpretation of insulin levels and his assertion that the babies’ collapses could only be explained by deliberate injection. His testimony was presented as authoritative, given his status as a consultant paediatric endocrinologist and clinical director for paediatrics at UCLH, as well as his honorary role at Great Ormond Street.

However, the Guardian has now confirmed that Hindmarsh’s contract with UCLH had been terminated in July 2022, four months before he gave evidence. Cheshire police say he did not disclose this either. When questioned in court by lead CPS barrister Nick Johnson KC about his honorary consultancy at Great Ormond Street, Hindmarsh did not clarify that his employment had already ended. The omission is now being described by legal experts as highly significant, given the weight placed on his testimony.

The situation escalated further when Great Ormond Street referred its concerns about Hindmarsh to the General Medical Council (GMC). The regulator opened a fitness‑to‑practise investigation on 25 November 2022—the very day Hindmarsh first appeared as an expert witness in the Letby trial. UCLH subsequently made its own referral. Hindmarsh was informed of the GMC investigation on 30 November. It was not until 14 December 2022 that he disclosed the GMC probe to Cheshire police, who then notified the CPS. Both institutions say this was the first time they were made aware of any concerns regarding his professional conduct.

The jury, however, was never told that the expert whose evidence underpinned two of the most serious allegations against Letby was under active investigation by both his employer and the medical regulator. The GMC inquiry was never concluded because Hindmarsh voluntarily removed himself from the medical register in November 2024, a process known as voluntary erasure, which effectively halts any ongoing proceedings.

Legal specialists have expressed concern about the implications of these revelations. Glyn Maddocks KC, joint secretary of the all‑party parliamentary group on miscarriages of justice, said that transparency from expert witnesses is essential to maintaining the integrity of the justice system. He noted that the rules are clear: experts must disclose anything that could affect how their evidence is perceived. An internal investigation into competence, he said, would certainly fall into that category. Another senior barrister, Tim Green KC, emphasised that while he could not comment on the specifics of the Letby case, an expert facing an adverse internal report would normally be expected to disclose it to the legal team instructing them.

Letby, a former neonatal nurse at the Countess of Chester Hospital, was convicted in 2023 and 2024 of murdering seven babies and attempting to murder seven others. She has consistently maintained her innocence. In February last year, her lawyer, Mark McDonald, submitted an application to the Criminal Cases Review Commission (CCRC), arguing that the convictions were unsafe. The application is supported by 27 experts, including a panel led by Canadian neonatologist Dr Shoo Lee, who contend that the medical evidence presented at trial was flawed and that the babies’ deaths and collapses were the result of natural causes and substandard care rather than deliberate harm.

McDonald has said he will now submit Hindmarsh’s non‑disclosure as further evidence to the CCRC. He described the failure to reveal the hospital investigation and contract termination as astonishing, given the central role Hindmarsh played in the prosecution’s case. He argued that the omissions raise serious questions about the expert’s credibility and integrity, and that the jury should have been made aware of the circumstances surrounding his professional standing.

The CPS has confirmed that it was not informed of any issues regarding Hindmarsh until December 2022, weeks after he had already given evidence. Cheshire police have echoed this account. Both institutions have declined to comment further while the CCRC review is ongoing. A representative for Hindmarsh said only: “We have no comment at this time.”

The revelations come at a moment when public confidence in the Letby verdicts is increasingly divided. While many families of the affected infants remain steadfast in their belief that justice was served, a growing number of medical professionals and legal analysts argue that the case may represent one of the most significant miscarriages of justice in modern British history. The role of expert witnesses—how they are selected, scrutinised, and monitored—has become a central point of debate.

The CCRC’s review is expected to be lengthy and complex, given the volume of medical evidence and the number of experts now challenging the prosecution’s case. If the commission concludes that the non‑disclosure of the investigation into Hindmarsh could have affected the safety of the convictions, it may refer the case back to the court of appeal. Such a move would reignite national debate and place renewed scrutiny on the processes that led to Letby’s conviction.

For now, the questions continue to mount. Why was the investigation into Hindmarsh not disclosed sooner? Should the jury have been informed? And what does this mean for the reliability of the expert evidence that helped secure Letby’s conviction? As the CCRC continues its work, the answers may determine not only the future of one of Britain’s most notorious criminal cases but also the standards by which expert testimony is judged in courts across the country.

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