The nurse was found guilty of murdering seven babies and attempting to murder six other infants while working on the hospital's neonatal unit between June 2015 and June 2016.

Consultant paediatrician Dr Dewi Evans, who gave evidence as an expert witness during her 10-month trial, was asked to look at cases where babies had died or collapsed unexpectedly on the unit during this period.

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Dr Evans said there were three inquiries prior to his investigation, with one carried out by two consultant paediatricians and two nurses from the Royal College of Paediatrics and Child Health.

The investigation was organised by hospital management, but Dr Evans says the "terms of reference did not allow the clinical notes of the babies who had collapsed".

Speaking to Sky's Katerina Vittozzi, Dr Evans said Letby's colleagues had expressed concerns about baby deaths during her shifts very early on but "nobody was listening to them".

The consultant paediatrician says this doesn't surprise him after 30 years of working on clinical negligence cases.

He said: "Those of us who deal with child abuse cases, usually the sentence of a negligent parent, we say that these are parents who are unable to distinguish their own needs, from the needs of that child or the needs of their children.

"And I think that health managers are exactly the same. They are unable to distinguish their own needs from the needs of the public or the needs of the patient. And this is endemic, you know, this always happens."

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'They're still in denial'

Asked whether the Countess of Chester Hospital has a case to answer after the deaths, Dr Evans said: "I think they're still in denial to be honest with you. I think they failed.

"That is not a matter for doctors, that is a matter for the police and other organisations."

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Dr Evans said when he began investigating the baby deaths and collapses he found that "a number of them" could not be explained on the "basis of any natural problem".

Some had collapsed due to an embolism after they had been injected with air, while others had been overfed with a "huge amount of milk".

Dr Evans said the "smoking gun" was when there was "no doubt" two babies had been "poisoned" after being found to have very high levels of insulin in their blood.

Jane Tomkinson, acting chief executive officer at the Countess of Chester Hospital NHS Foundation Trust, said: "Following the trial of former neonatal nurse Lucy Letby, the Trust welcomes the announcement of an independent inquiry by the Department of Health and Social Care.

"In addition, the Trust will be supporting the ongoing investigation by Cheshire Police.

"Due to ongoing legal considerations, it would not be appropriate for the Trust to make any further comment at this time."

Letby is due to be sentenced on Monday.