Lucy Letby case expert witness was under fitness to practise investigation during trial | Lucy Letby

A doctor who gave crucial expert evidence about insulin poisoning for the prosecution of the nurse Lucy Letby was under investigation by the medical regulator at the time due to serious concerns about his fitness to practise.

The General Medical Council (GMC) opened an investigation into concerns about Prof Peter Hindmarsh, including that he had harmed patients, on the first day he gave evidence at Letby’s trial in late 2022.

The GMC investigation was still continuing when Hindmarsh gave evidence for a second time at the Letby trial three months later. Great Ormond Street hospital reported Hindmarsh to the GMC after a formal investigation led by his main employer, University College London hospitals trust (UCLH).

The jury in the trial of the nurse, who was convicted of murdering babies in the Countess of Chester hospital’s neonatal unit, was never informed about any investigation into Hindmarsh, one of the prosecution’s key witnesses.

While the GMC conducted its investigation, and during some of the period when Hindmarsh gave evidence, a medical tribunal ordered severe restrictions on his work, saying that he “may pose a real risk” to members of the public. The tribunal also considered the allegations about Hindmarsh “may have the potential to impact on his ability to act as an expert witness”.

Nevertheless, the tribunal permitted him to continue giving expert evidence for the prosecution of Letby. The Crown Prosecution Service told the defence it would oppose any attempt to inform the jury of the GMC investigation, on the basis that the allegations had not reached a final adjudication.

Ultimately the GMC investigation was never concluded, because Hindmarsh removed himself from the GMC register, a process known as “voluntary erasure”. That effectively ended the investigation, and there was no regulatory finding against him.

Details of the allegations against Hindmarsh at the time of his evidence have been uncovered in an investigation by the Guardian.

Letby was convicted of murdering seven babies and attempting to murder seven others, over two trials in 2023 and 2024. She was sentenced to 15 whole-life terms in prison. Court of appeal judges turned down her applications to appeal. She has always maintained she is innocent, and many of her supporters believe she was scapegoated for medical failings on the unit.

Since the convictions, dozens of leading UK and international medical and scientific experts have argued that the prosecution’s medical case, including Hindmarsh’s evidence, was wrong. Dr Shoo Lee, a renowned Canadian neonatologist who argues that the prosecution misrepresented his own research, last year delivered findings of a 14-member expert panel. They found unanimously that the babies died or collapsed due to natural causes and poor care on the unit, that there had been no evidence of murders, nor insulin poisoning or any other deliberate harm.

In February last year Letby’s lawyer, Mark McDonald, applied to the Criminal Cases Review Commission (CCRC), which examines possible miscarriages of justice, to have her case sent back to the court of appeal. The CCRC is reviewing the application, which is supported by the reports of 27 leading experts, including Lee’s panel.

‘Multiple and wide-ranging concerns’

Hindmarsh appeared twice as a key witness for the prosecution during Letby’s first trial, which took place between October 2022 and August 2023, thought to have been Britain’s longest ever murder trial.

A professor and consultant paediatric endocrinologist – a specialist in hormones – Hindmarsh also had extensive clinical experience working with children. He had practised at UCLH hospitals for decades, and was also an honorary consultant at Great Ormond Street.

He first gave evidence on 25 November 2022. He was an expert witness for the prosecution’s case that Letby attempted to murder two babies, referred to as F and L. Hindmarsh’s evidence supported the case that both babies had been poisoned with insulin injected into their fluid feed bags.

But the jury was never told that in the months leading up to the trial, Hindmarsh had been facing allegations at the two hospitals that threatened to tarnish his reputation and undermine his credibility. He was, by then, still at UCLH, but no longer working at Great Ormond Street; his contract had been terminated four months earlier, in July 2022.

Contacted by the Guardian, the children’s hospital declined to say whether the termination of the contract was related to the allegations of clinical failings that were ultimately referred to the GMC. A representative for Hindmarsh said he had no comment to make in response to questions from the Guardian.

When he was first introduced in court by the prosecution’s lead barrister, Nick Johnson KC, Hindmarsh confirmed he was a consultant at UCLH. Johnson then asked him: “Are you an honorary consultant at Great Ormond Street hospital though?” Hindmarsh replied: “Yes. At that stage, yes.”

It is unclear what Hindmarsh meant, since Johnson had not referred to any previous stage or phase in his career. Hindmarsh did not say his contract at Great Ormond Street had been terminated, and this was never clarified to the jury.

Neither were they informed of the allegations of professional misconduct against him. In the months before he gave evidence, UCLH had been leading a formal investigation into Hindmarsh.

Then, on 15 November 2022, Great Ormond Street, which had been feeding into the UCLH-led investigation, referred “multiple and wide-ranging concerns about Prof Hindmarsh’s practice” to the GMC. The regulator opened its own formal investigation 10 days later, on 25 November. That was the same day Hindmarsh first gave evidence at the trial.

Between Hindmarsh’s first and second appearances as an expert witness, there were further developments. On 30 November, he was informed of the GMC investigation prompted by Great Ormond Street. The following month, on 21 December 2022, UCLH reported “similar clinical concerns” about Hindmarsh to the GMC, indicating that he had been suspended pending a return to work under “close supervision”.

According to leaked documents seen by the Guardian, the allegations raised about Hindmarsh included “identified cases where harm to patients has been alleged”, and concerns including his “diagnosis and treatment of patients”, “use of treatments in unusual age groups, without adequate monitoring”, “inappropriate investigations” and inadequate documentation.

By early January 2023 the tribunal had renewed restrictions that had been placed on Hindmarsh the previous month, after an application by the GMC. The tribunal stated: “In all the circumstances the tribunal considers that there is information to suggest that Prof Hindmarsh may pose a real risk to members of the public, if he were permitted to return to unrestricted clinical practice, given the number and nature of the concerns, involving paediatric [child] patients.”

In its interim order, the tribunal said Hindmarsh must be restricted to work only at UCLH, and had to be supervised there in all his posts.

It was against this backdrop that Hindmarsh applied to the tribunal for permission to continue working as an expert witness in courts. His representative argued this work was “plainly not relevant to the very niche concerns in this referral”.

The tribunal’s decision in January stated: “The tribunal is mindful that the concerns raised about Prof Hindmarsh’s practice include his documentation, his diagnosis and management of patients. It considers that these areas of Prof Hindmarsh’s practice may have the potential to impact on his ability to act as an expert witness.”

Nevertheless, the GMC did not object to Hindmarsh being an expert witness, and the tribunal allowed it. The only condition imposed was that Hindmarsh had to inform any party instructing him that he was under GMC investigation.

This was an obligation Hindmarsh was already under, since the criminal procedure rules require expert witnesses to disclose to the party instructing them anything “that might reasonably be thought capable of undermining the expert’s opinion or detract from the credibility or impartiality of the expert”.

That would suggest Hindmarsh may have been obliged to report to the prosecution details of the earlier UCLH-led investigation, which preceded his appearance on the witness stand in late November 2022. A source familiar with the prosecution said the CPS was not made aware of “any” investigation until December 2022, which suggests it was not informed of the UCLH-led inquiry before he first gave evidence.

Insulin evidence contested

Hindmarsh first formally told the police that he was subject to a GMC investigation on 14 December 2022, two weeks after Great Ormond Street told him it had referred him to the GMC. The CPS then waited a further two months before informing Letby’s then barrister, Ben Myers KC, about the investigation into one of its key witnesses. It was formally disclosed just four days before Hindmarsh was due to give his second day of evidence.

The prosecuting barrister, Johnson, told the defence he would oppose the jury being told anything about the GMC investigation, on the grounds that it had not reached a final adjudication. The Guardian asked Johnson about that position. He replied via a representative: “We do not conduct cases through journalists.”

In response to similar questions, a CPS spokesperson said: “We do not accept that the jury was misled about the qualifications or experience of the expert witness in this case.”

It is unclear why, after it was informed about the GMC investigation into Hindmarsh, Letby’s defence did not make an application to the judge, James Goss, for the jury to be informed. Myers, her lead barrister at the time, told the Guardian he could not answer any questions due to continuing client confidentiality.

The GMC did not directly respond to questions about whether it should have prevented Hindmarsh from giving further evidence.

Hindmarsh made his second appearance at the Letby trial on 24 February 2023. The jury remained uninformed about the GMC investigation, the UCLH-led investigation, the restrictions on him practising, or any of the concerns at the two hospitals.

Hindmarsh’s evidence for the prosecution appears to have been pivotal in the trial. The prosecution said that the insulin cases were “incontrovertible” evidence that someone was deliberately endangering the babies and that this could inform the jury’s view about other babies’ deaths.

In summing up, the judge also told the jury that if they were sure about deliberate harm in any one case, they were entitled to infer the same in other babies, even if the precise cause was not known. These insulin cases were the first on which the jury reached a guilty verdict, and were two of only three guilty verdicts that were unanimous.

The insulin cases stood out for other reasons, too. Unlike other parts of the prosecution, which were based on circumstantial evidence, the case presented to the jury was that the allegations of insulin poisoning were based on scientific blood test results.

Hindmarsh told the court that these tests and the medical records of babies F and L showed they suffered from hypoglycaemia – low blood sugar – because they had been poisoned with insulin most likely inserted into intravenous bags of fluids. The prosecution alleged that Letby had injected insulin into the bags, although there was no direct or forensic evidence that she or anybody else had done so.

Experts who are now arguing that Letby’s convictions are unsafe, including those who have submitted reports in support of her application to the CCRC, have contested Hindmarsh’s insulin evidence and the prosecution’s case on numerous points. They have said the type of tests used to measure insulin are known to produce rogue results and should never have been relied on.

They also say that Hindmarsh’s calculations are wrong and the prosecution theory that insulin was delivered via the feed bags is not plausible. And they note that Hindmarsh’s evidence did not inform the jury of plausible alternative explanations for the babies’ hypoglycaemia, which they argue persisted because of poor medical care.

The Guardian asked Hindmarsh detailed questions about his evidence, the GMC and UCLH-led investigations into the concerns raised about his practice, and whether he made adequate disclosure of it before the trial. A spokesperson replied that he had “no comment to make”. A GMC spokesperson said: “Dr Peter Hindmarsh is no longer registered with the GMC, having relinquished his registration on 14 November 2024.”’