The crimes of child serial killer Lucy Letby will be examined in a public inquiry.

The Government ordered a probe after the nurse was last week found guilty of murdering seven babies and trying to murder six more.

It will investigate the events on the Countess of Chester Hospital’s neonatal unit between 2015 and 2016 to ensure “vital lessons are learned”, ministers said.

But concerns have been raised over the decision not to put the probe on a statutory footing, with pressure growing on the Government to strengthen it.

Here, PA looks at statutory and non-statutory inquiries.

– What is a public inquiry?

It is a major investigation, convened by a Government minister, looking into a matter of public concern.

It seeks to find out what happened, why it happened, who is to blame and what can be done to stop it from happening again.

Although funded by the Government, a public inquiry runs independently.

The minister initiating the official probe appoints the chairperson, who is often a former judge.

Before the investigation begins, the terms of reference are prepared to set out its scope and purpose, with people affected by the issue often consulted.

Once the inquiry is complete, the chairperson or panel will produce a report with their/its findings and any recommendations.

Ongoing public inquiries are looking into the Grenfell Tower fire, the NHS infected blood scandal and the UK’s handling of the coronavirus pandemic.

An inquiry can be convened on a statutory or non-statutory basis.

– What is a statutory inquiry?

Commissioned under the Inquiries Act 2005, which sets out the powers and rules for how it operates, a statutory inquiry has the power to compel a person to give oral evidence, provide a written statement or produce documents relating to the issues being examined.

It is a criminal offence to fail to comply with such a request or destroy the required documents.

The chairperson also has the power to take evidence under oath, which means a witness could commit a criminal offence if they give evidence they know to be false.

– How does a non-statutory inquiry differ?

It lacks the power to compel witnesses to attend, produce documents or give evidence under oath.

Instead, a non-statutory inquiry relies on the co-operation of people and organisations involved, although they may be under significant political or reputational pressure to participate.

Witnesses’ refusal to participate could harm public trust in the process and limit the inquiry’s ability to produce its report.

A non-statutory inquiry does not have to meet the requirements of the Inquiries Act 2005 and can therefore decide its own procedures and protocols.

For example, the chairperson can choose to hear evidence in private when matters are sensitive – like when they relate to national security.

The greater flexibility may allow the inquiry to progress at a quicker pace than a statutory one.

But the discretion afforded to the chairperson of a non-statutory inquiry could mean they do not meet the same standards of public accountability as their statutory counterparts.

– What has the Government said about the inquiry into Letby’s crimes?

Health Secretary Steve Barclay last Friday ordered an independent inquiry on a non-statutory footing amid concerns a statutory one could drag on.

Children’s minister Claire Coutinho argued it would be “much quicker” than a statutory probe.

Rishi Sunak refused to be drawn on the issue on Monday, saying he wants the victims’ families to get answers “as quickly as possible”, the process to be transparent and for lessons to be learned from failures in the case.

However, after mounting calls for the investigation to be strengthened, Downing Street indicated it could be upgraded.

The Prime Minister’s official spokesman said: “We are focused on the outcomes. The most important thing is to make sure families get the answers they need and that it’s possible to learn the lessons, that it’s done transparently and that it happens as quickly as possible.

“And that’s crucial. And obviously, we will have an inquiry on the right footing to achieve that.”

Education Secretary Gillian Keegan on Tuesday said a statutory inquiry is “on the table”.

“But there are pros and cons to the two types of inquiry, so when the chair works with them (the families) on the terms of reference that will be something that they can input to them,” she said.

A chairperson has not yet been appointed and No 10 could not say when the terms will be published.

– What are the arguments for the inquiry to be upgraded?

Labour leader Sir Keir Starmer has called for a statutory inquiry, saying what it “gives you is the power to order documents, to order witnesses to come forward so we get the fullest, proper, comprehensive analysis of what went wrong here”.

Steve Brine, the Conservative chairman of the Health Select Committee, said some key witnesses may not be willing to co-operate with a non-statutory inquiry, which he said could drag on for years and “disappear down a rabbit hole”.

Dame Christine Beasley, a former chief nursing officer, said if witnesses “can opt out of it if they want to”, “relatives and patients will not feel that they’ve got to the bottom of it”.

Paediatrician Dr Stephen Brearey, who blew the whistle on Letby in 2015, said the victims’ parents “deserve” a probe “with the most wide-ranging and statutory powers”.

Lawyers representing families of some of the babies attacked by Letby said a non-statutory public inquiry into her killing spree is “inadequate” and needs to have a “statutory basis to have real teeth”.

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