The NHS in England has been “broken” by successive Conservative-led governments – and the state it is now in is “unforgiveable”, Sir Keir Starmer has told the BBC.

In his first major interview in Downing Street, the prime minister said a review of the health service to be published on Thursday finds changes to the NHS were “hopelessly misconceived”.

He said austerity in the coalition years, and then the Conservative government’s handling of the pandemic, left the NHS in an “awful position”.

Speaking on Sunday with Laura Kuenssberg, Sir Keir added that the review by an eminent surgeon, Lord Darzi, is expected to reveal too many children “are being let down” by the health service.

“Everybody watching this who has used the NHS, or whose relatives have, knows that it’s broken,” Sir Keir said. “That is unforgivable, the state of our NHS.”

In response to Sir Keir’s comments, shadow health secretary Victoria Atkins said after 14 years in opposition, “Labour’s instinct is to politicise children’s health, rather than provide solutions and reform our NHS”.

The prime minister said the report will claim the current problems come from historical factors, including “hopelessly misconceived” reforms pursued by the former Conservative Health Secretary Andrew Lansley in 2012.

In particular, the report is expected to reveal increased wait times, falling vaccination rates, and other worsening health outcomes for children. The findings are expected to show:

• More than 100,000 infants were left waiting for more than six hours in A&E departments in England last year
• Wait times for infants rose 60% over the past 15 years
• Around 800,000 children and young people are on NHS waiting lists for hospital treatment, with 175,000 waiting between six and 12 months and 35,000 waiting for more than a year
• ADHD prescription medications for children and young people rose 10% annually between 2004 and 2023
• Hospital admissions for children and young people with eating disorders rose 82% since 2019 to 2020

It is also expected to find that children from the most deprived backgrounds were twice as likely to be obese by reception age.

In the poorest communities, the report finds, nearly one-in-three children is obese by Year 6.

Meanwhile, the report says life-threatening and life-limiting conditions among children are up 40% over the past two decades.

The full contents of the Darzi report will be published on Thursday.

As Sir Keir puts it, the report was to provide the diagnosis so that a longer term cure could be worked out.

Some of Lord Darzi’s report has been put out early by the government with eye-catching findings, and his conclusion that there were “real concerns” over the ability of the NHS to deliver quality care.

But there will be much more in the report to be published in the next few days. What will it say, for example, about overstretched GP services? Or retention and recruitment of staff? It will undoubtedly set out more problems and challenges.

Sir Keir pinned the blame for the problems on the Tories, in an echo of the government’s criticisms of its economic inheritance, and argued only Labour can bring the reform the government needs.

“It’s the last government that broke the NHS,” Sir Keir said. “Our job now through Lord Darzi is to properly understand how that came about and bring about the reforms.”

He said that started with the first step of funding 40,000 out-of-hours NHS appointments each week to cut waiting lists.

There are questions over how long Labour can keep blaming the Conservatives and when scrutiny will turn to their own performance against NHS targets.

Sir Keir appeared to acknowledge this, saying: “We’ve got to do the hard yards of reform as well.

“And as I say, I think it’s only a Labour government that can do the reform that our NHS needs, and we’ll start on that journey.”

In the wide-ranging interview in Downing Street’s Cabinet Room, Sir Keir also discusses the summer riots, Grenfell disaster, public finances and his upcoming second visit to the White House.

Watch the full interview from 09:00 BST on Sunday on BBC One or BBC iPlayer.