The official inquiry into the murders committed by Lucy Letby could be upgraded to compel witnesses to give evidence, Downing Street has indicated. Rishi Sunak has come under growing pressure from victims’ families and experts who want the investigation strengthened to become a statutory inquiry, giving its chair full legal powers to summon witnesses. The prime minister, on a visit in North Yorkshire on Monday, refused to be drawn on the issue, saying his priority was that the families got answers “as quickly as possible” and that lessons were learned from failings around the case. But the Guardian understands that No 10 is open to the idea of a statutory inquiry after Letby was handed a whole-life prison sentence for the murders of seven babies in her care at the Countess of Chester hospital and the attempted murders of six more. The government has been under growing pressure to rethink its approach to the inquiry into events at the hospital’s neonatal unit between 2015 and 2016, launched last week on a non-statutory basis amid concerns that a statutory investigation could drag on. Dr Dewi Evans, the prosecution’s lead medical expert in the Letby trial, told the Guardian: “A non-statutory inquiry is a complete waste of time and money and it should be statutory where it is public and people are required to give evidence on oath. “Anything else is a waste of time and money. It’s indicative of the government wanting to be seen to be doing something instead of actually doing something that could lead to significant changes.” The former chief nursing officer Dame Christine Beasley told the BBC: “I think what a statutory inquiry will do is compel people to come and give evidence where in an independent inquiry people can opt out of it if they want to. “So I really understand parents and families wanting to make sure we get to the bottom of whatever happened there so that we can actually learn. “I would go down on the side of a statutory inquiry would be better because whatever the outcome of the independent inquiry is, I feel that relatives and patients will not feel that they’ve got to the bottom of it.” The Labour leader, Keir Starmer, told Sky News: “It has to be a statutory inquiry. I don’t think that needs to hold things up. We could get on with that very quickly.” The former health secretary Matt Hancock added his voice to those calling for a statutory inquiry. He told the Guardian: “This is without question one of the most monstrous crimes in modern British history. What makes it worse is the evidence that some of these evil murders could have been prevented. “We need an urgent, full statutory inquiry with powers to compel witnesses to attend. It’s so important to fully understand what happened, learn lessons for the NHS and prevent a tragedy like this ever happening again.” The Department of Health and Social Care originally launched a non-statutory inquiry in the belief that it would be quicker. However, the prime minister’s official spokesman said on Monday that the government had not ruled out holding a statutory inquiry. He added: “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. “That’s crucial. And obviously, we will have an inquiry on the right footing to achieve that.” On his visit to a nursery school, Sunak told reporters: “I think the important thing for the inquiry to do is make sure that families get the answers that they need, that it is possible for us to learn the lessons from what happened, everything conducted transparently and to happen as quickly as possible. “Those are the objectives that we want for the inquiry and we’ll make sure that it’s set up to deliver on those aims.” In June the government U-turned on its refusal to grant statutory powers to the inquiry into the deaths of almost 2,000 mental health patients across NHS trusts in Essex after pressure from bereaved relatives and the chair of the inquiry, who said she could not do her job without them.