Anyone who believes the police case against Lucy Letby ‘should have their head examined’, a medical expert has insisted in a new book about the neonatal nurse serving 15 whole life sentences for murder and attempted murder.

After interviewing more than 60 specialists for Reasonable Doubt: Examining The Case Of Lucy Letby, investigative author Christopher Morris raises questions about controversial claims that Letby poisoned the babies with insulin.

Letby was found guilty of the murders of seven babies and the attempted murders of seven others at the Countess of Chester Hospital in Cheshire between 2015 and 2016. 

The juries reached their verdict despite the absence of forensic or CCTV evidence and the lack of a convincing motive.

Independent reviews later found that the neonatal unit was understaffed and working beyond capacity.

Over the past two years, The Mail on Sunday has highlighted how Letby was convicted on the basis of contested statistical probabilities and increasingly disputed theories about how she might have inflicted harm on the babies.

In his new book, Mr Morris writes: ‘A very different story than the one set out in court is emerging and it is important this story is told, both to right a possible miscarriage of justice and to highlight that serious mistakes made in the management and care of infants may not have been properly addressed.’

He quotes neonatologist Professor Shoo Lee, who convened an international panel of medical experts to produce fresh reports about the evidence cited in court, as saying: ‘Anyone who reads the reports and still thinks that Lucy Letby is guilty should have their head examined.’

The prosecution’s case centred on the fact that two infants under her care were found to have ‘abnormally high’ insulin levels.

But peer-reviewed research by diabetes expert Prof Geoff Chase has found that insulin in newborns can be sky-high without foul play if infection is present. 

His work with colleague Helen Shannon could be used by lawyers to argue Letby could not have poisoned the babies with the ‘tiny’ amounts of insulin she is said to have used.

Last month, this newspaper revealed internal documents from the Countess of Chester showing managers were concerned about the ‘bullying’ behaviour of two doctors towards Letby after she highlighted apparent failures of care in their neonatal unit, triggering her removal from the wards.

After Letby launched a grievance procedure against Dr Stephen Brearey and Dr Ravi Jayaram, the hospital found in her favour – but by then the doctors had contacted police with their concerns about her. The juries in the resulting trials were unaware of this.

Dr Jayaram was the only medical witness at Letby’s two trials able to point to behaviour directly linking her to babies’ deaths, testifying she was standing over Baby K’s cot as the girl deteriorated and that she did not call for help. 

Last year the MoS revealed an email disclosed to Letby’s defence team only after she had been jailed had contradicted his claims she was caught ‘red-handed’ with a baby who died. 

Her lawyers have submitted an application to the Criminal Cases Review Commission citing a miscarriage of justice.

• Reasonable Doubt: Examining The Case Of Lucy Letby, by Christopher Morris (Cinto Press), will be published on July 9.