Three former justice secretaries last night added their weight to growing pressure to strengthen the official inquiry into Lucy Letby's sickening crimes.

The trio joined others calling for a probe to be put on a statutory footing to give the public greater confidence and avoid accusations of an NHS 'cover-up'.

And Labour leader Sir Keir Starmer joined the chorus, saying a statutory inquiry was the only way to get the 'fullest, proper, comprehensive' understanding of what went wrong and when.

Government sources said ministers were looking at 'all options' for upgrading the inquiry and Prime Minister Rishi Sunak did not rule it out.

As it stands, the probe announced after Letby's convictions on Friday is non-statutory, meaning it will not have the power to force witnesses to appear before it or present certain documents.

Baby killer nurse Lucy Letby, 33, was convicted of murdering seven premature babies and attempting to murder six more. A judge gave her 14 whole-life orders

Labour leader Sir Keir Starmer says a statutory inquiry was the only way to get the 'fullest, proper, comprehensive' understanding of what went wrong and when

Children's minister Claire Coutinho defended the existing set-up, saying it 'makes more sense' because it could conclude faster.

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She added: 'I think speed is of the essence to make sure that expectant parents across the country can feel assured that they know that there are steps in place to make sure that this won't happen again.'

But Sir David Lidington, who served as justice secretary under Theresa May, said the findings of a full-blown judge-led, statutory inquiry would command greater public confidence.

He also backed calls to appoint a foreign medical expert to sit alongside a judge to avoid it being influenced by pro-NHS bias.

He told the Daily Mail: 'I just think that because of the issue of trust that is at stake here, we should have a statutory inquiry and that it should include somebody who is from a different jurisdiction who has not got any [NHS] service history, somebody who is genuinely independent or who has no axe to grind.'

It has been alleged that some NHS managers ignored warnings from Letby's colleagues that she was killing babies.

Labour peer Lord Falconer, who was Sir Tony Blair's justice secretary, said there was a risk that a non-statutory inquiry would allow these to be covered up.

Sir David Lidington, who served as justice secretary under Theresa May, said the findings of a full-blown judge-led, statutory inquiry would command greater public confidence

It has been alleged that some NHS managers ignored warnings from Letby's colleagues that she was killing babies. Labour peer Lord Falconer (pictured), who was Sir Tony Blair's justice secretary, said there was a risk that a non-statutory inquiry would allow these to be covered up

Jack Straw, who succeeded Lord Falconer under Gordon Brown, believes 'a non-statutory inquiry is not appropriate for circumstances like these, and in my experience is likely to create more problems than it avoids'

He said: 'The inquiry can compel the production of people to give evidence and documents and if you look at what's happening at the moment, with blame being traded – although no doubt the Government would ensure the institutions such as the hospitals and the NHS co-operated, they couldn't do that in relation to individuals who are no longer employed.'

Jack Straw, who succeeded Lord Falconer under Gordon Brown, said: 'A non-statutory inquiry is not appropriate for circumstances like these, and in my experience is likely to create more problems than it avoids.

'It may have to spend years putting draft conclusions to witnesses who had not been properly cross-examined on specific but relevant issues during the evidence gathering part of the inquiry.

'Statutory inquiries may themselves drag on, but overall they are better.'