Lucy Letby witness was under investigation for 'harming patients' during trial

He remained under investigation when he returned to give evidence three months later in February 2023.

Jurors were not told about the probe or that restrictions had been placed on his medical work, according to a report by The Guardian.

The GMC tribunal allowed him to testify for the prosecution, while the Crown Prosecution Service (CPS) told the defence it would oppose attempts to inform the jury about the investigation into the University College London Hospitals NHS Foundation Trust employee.

Documents seen by The Guardian allege concerns raised during the tribunal included the “diagnosis and treatment of patients”, the “use of treatments in unusual age groups without adequate monitoring”, and poor documentation.

The material also reportedly identified cases “where harm to patients has been alleged”, with Prof Hindmarsh ordered to work only at UCLH and to be supervised in all his roles.

The investigation never reached a conclusion after Prof Hindmarsh removed himself from the GMC register in a process known as voluntary erasure, according to The Guardian.

Letby was convicted of murdering seven babies and attempting to murder seven others while working at the Countess of Chester Hospital, receiving 15 whole-life prison sentences.

She has always maintained her innocence and has been supported by a number of international experts.

Last year, Canadian neonatologist Shoo Lee presented findings from a panel of 14 specialists who reviewed the case.

The group concluded that the babies died or collapsed due to natural causes and poor care rather than deliberate harm.

The panel assessed four of the seven deaths individually and identified alternative explanations in each case.

Letby’s lawyer, Mark McDonald, has since submitted the case to the Criminal Cases Review Commission in an effort to have the convictions reconsidered.

The application is backed by 27 experts, including members of Dr Lee’s panel.

Prof Hindmarsh, a consultant paediatric endocrinologist, gave evidence twice during the trial.

He had worked for decades at UCLH and also served as an honorary consultant at Great Ormond Street Hospital.

During his first appearance on 25 November 2022, he supported the prosecution’s claim that Letby had deliberately injected insulin into the feeding bags of two infants.

However, several experts have disputed that evidence, arguing that the tests used to measure insulin can produce unreliable results.

They have also challenged his calculations and said the theory that insulin was delivered via a feed bag is implausible.

A spokesperson for the CPS told The Times it did not accept that the jury had been misled about the expert’s qualifications or experience, adding that any challenge to the safety of the convictions “is a matter for the courts”.

A representative for Prof Hindmarsh told The Guardian 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.”