Lawyers for child serial killer Lucy Letby will make a fresh bid to challenge her convictions on the grounds that the lead prosecution medical expert at her trial was “not reliable”.

Her barrister, Mark McDonald, said he would immediately seek permission from the Court of Appeal to take the “exceptional but necessary decision” to apply to reopen her case.

Speaking at a press conference in central London, Mr McDonald said that “remarkably” Dr Dewi Evans had changed his mind over the mechanism of death involving three of Letby’s murder victims.

He said: “The defence will argue that Dr Evans is not a reliable expert, and all the convictions are not safe.”

Letby, 34, from Hereford, is serving 15 whole-life orders after she was convicted at Manchester Crown Court of murdering seven infants and attempting to murder seven others, with two attempts on one of her victims, between June 2015 and June 2016.

The defence will argue that Dr (Dewi) Evans is not a reliable expert, and given that he was the lead expert for the prosecution, we say that all the convictions are not safe

The former nurse has lost two bids this year to challenge her convictions at the Court of Appeal – in May for seven murders and seven attempted murders and in October for the attempted murder of a baby girl which she was convicted of by a different jury at a retrial.

The Thirlwall Inquiry into how Letby was able to commit her crimes has heard evidence at Liverpool Town Hall since September and will resume in January, with findings expected to be published in autumn 2025.

In his statement to reporters, Mr McDonald said: “The primary grounds of appeal at the previous hearings related to the admissibility before the jury of the evidence of the lead prosecution expert Dr Dewi Evans.

“The defence argued twice at trial that Dr Evans’ evidence should be disregarded. This was refused by the trial judge.

“It was then later argued in the Court of Appeal and was refused in the Court of Appeal.

“Remarkably, Dr Evans has now changed his mind on the cause of death of three of the babies: Baby C, Baby I and Baby P.”

Mr McDonald continued: “Dr Evans had said to the jury that Lucy Letby had injected air down a nasal gastric tube and this had led to the death of the three babies.

“This was repeated to the Court of Appeal, who may have been misled when they ruled on the application for leave against the convictions.

“Dr Evans has also said that he has revised his opinion in relation to Baby C and has written a new report, a new report that he has given to the police, months ago now.

“Despite numerous requests, the prosecution has yet to give this report to the defence.

“The defence will argue that Dr Evans is not a reliable expert, and given that he was the lead expert for the prosecution, we say that all the convictions are not safe.”

Dr Evans, who gave expert evidence to the jury in Letby’s first trial, has previously given numerous media interviews in which he maintains her convictions are safe.

Dr Evans has been contacted for comment.

In May, the Court of Appeal dismissed Letby’s leave to appeal on all grounds – rejecting her argument that expert prosecution evidence was flawed

Mr McDonald added he also has reports from two neonatologists that he claims count as fresh evidence in the cases of Baby C and Baby O, with no evidence of deliberate harm.

He said those two reports would be contained in his submission this week to the Criminal Cases Review Commission (CCRC) to review Letby’s case but warned that avenue would “take a long time”.

The CCRC investigates potential miscarriages of justice and can refer cases back to the Court of Appeal for consideration.

He said: “CCRC can take years. I have one case with the CCRC that’s in its eighth year, and so they will take a long time. To deal with these issues, they may get their own experts to look at what we put in – months and months and years go by.

“My argument is the CCRC is there to look at fresh evidence. This is not fresh evidence. This is the lead prosecution expert who has changed his mind. And the Court of Appeal may not have been told the accurate picture as a result, that itself makes it unique.

“I have never known in 26 years of being a barrister, an expert change their mind a year after the convictions on the cause of death of what they said to the jury. That to me is astonishing.”

He added that Dr Evans gave his new opinions on the three deaths in a signed statement in response to a Channel 5 documentary broadcast earlier this year.

He said: “Now don’t get me wrong, I’m sure Dr Evans is still going to say that Lucy Letby is guilty and he has a different view or different hypothesis in relation to it.

“But the cause of death that was before the Court of Appeal is different now, according to Dr Evans, and I think that is a profound issue that needs to be relooked at.”

Letby was convicted of attacking infants in her care at the Countess of Chester Hospital’s neonatal unit by various means, including injecting air via feeding tubes, injecting air into the bloodstream, assault, force feeding with milk and poisoning with insulin.

A court order prohibits reporting of the identities of the surviving and dead children involved in the case.

Following the press conference, the Crown Prosecution Service said: “Two juries and three appeal court judges have reviewed a multitude of different strands of evidence against Lucy Letby.

“She has been convicted on 15 separate counts following two separate jury trials.

“In May, the Court of Appeal dismissed Letby’s leave to appeal on all grounds – rejecting her argument that expert prosecution evidence was flawed.”