The inquiry into serial killer Lucy Letby’s crimes will “fully investigate” how NHS whistleblowers were treated, Health Secretary Steve Barclay said.

Mr Barclay said he was engaging with the families affected by Letby’s “horrendous crimes” and that it was important that they had “full confidence” in the inquiry.

But he declined to say whether the inquiry would be given statutory footing, despite calls from a number of families involved.

Parliamentary and Health Service Ombudsman Rob Behrens and former home secretary Jack Straw have joined those calling for an inquiry into Letby’s crimes to be given a statutory footing, which would mean witnesses would be compelled to attend to give evidence.

Letby, 33, was sentenced to a whole-life term on Monday for the murder of seven babies and the attempted murders of six more.

Senior doctors at the Countess of Chester Hospital, where she carried out her year-long killing spree on the neonatal unit, raised concerns for months before she was finally taken off frontline duties.

Speaking to broadcasters, Mr Barclay said: “Firstly, I want to express my deepest sympathies for the families affected by the horrendous crimes that we’ve seen at Chester.

“That’s why we’ve launched an immediate inquiry, and talking to the Attorney General and colleagues across Government in terms of the appropriate chair of that inquiry.

“As the Prime Minister has said, we’ll ensure that the legal framework for that has the full confidence of the families affected and I’ll be engaging with them on that, whether that’s on a statutory or a non-statutory basis, to ensure that inquiry, looking at issues such as whistleblowers and other actions related to this case, are fully investigated.”

He added: “Clearly, there’s a whole range of questions that have been raised by the case, they need to be looked at fully through a detailed inquiry, we need to ensure that that inquiry has the full confidence of the families affected.

“That is why I’m engaging with those families about the right legal framework for that inquiry.

“It’s important that we get that set up in a way that has the full confidence of the families and it’s the families that I am absolutely focused on in ensuring that their voices are heard.”

Mr Straw told the BBC Radio 4 Today programme: “You can shame a lot of (witnesses) but you can’t shame them all, and there may be witnesses in the Letby case who really ought to be on the stand, who are the most vulnerable in terms of the positions they have taken, and who won’t be bothered about being shamed – they would rather be shamed for their absence than actually appear on the stand.”

In a letter to Mr Barclay, Mr Behrens said: “Only a statutory inquiry can provide the strong legal powers necessary to compel witnesses and the release of evidence.

“The inquiry should have all possible levers available to it to get to the truth. The families involved deserve no less.”

On Tuesday Tamlin Bolton, a solicitor for law firm Switalskis, which is representing the families of seven of Letby’s victims, said that a statutory inquiry into Letby’s crimes is “exactly” what the families of her victims want.

The hospital saw a significant rise in the number of babies suffering serious and unexpected collapses in 2015 and 2016.

Letby’s presence when collapses took place was first mentioned to senior management by the unit’s head consultant in late June 2015.

Concerns among some consultants about Letby increased and were voiced to hospital bosses when more unexplained and unusual collapses followed, her trial at Manchester Crown Court heard.

But Letby was not removed from the unit until after the deaths of two triplet boys and the collapse of another baby boy on three successive days in June 2016.

She was confined to clerical work but registered a grievance procedure, which was resolved in her favour, and was due to return to the unit in March 2017.

The move did not take place as soon after police were contacted by the hospital trust.