Andy Burnham has pledged to intervene as early as childhood to tackle youth unemployment before a watershed review, promising “a root-and-branch rethink of how we support childhood in the modern world”.

Burnham said the government would intervene at all the stages of life in which young people fell behind, and “long before they find themselves out of work and reliant on the state”, including providing more opportunities for vocational training in schools.

Writing in the Guardian, the prime minister said ministers’ response to Alan Milburn’s long-awaited review into the crisis of youth unemployment in the UK would not be “a traditional … reform” but “societal and generational”.

He promised to reduce the number of Neets – 18 to 24-year-olds not in employment, education or training – which topped a million this year for the first time in more than a decade.

Hoping to head off opposition from leftwing MPs in his own party, who rebelled to block Starmer’s welfare changes last summer, Burnham said the government would “invest in our young people and give them a proper chance to get on”, but said the support “will have to come with responsibilities”.

“If we give young people genuine opportunities to learn, train and work, we should expect them to take them where they can. Benefits must become the backstop, not the starting point,” said Burnham.

Milburn’s long-awaited report on youth unemployment will promise almost half a million job and education opportunities within a decade, but will also advise sweeping changes to the benefits system for under-25s.

Some young people will lose their personal independence payments and the right to claim the health element of universal credit, and instead will get a new youth allowance paid at the standard rate of universal credit.

The government has also announced it will expand a taxpayer-funded scheme aimed at helping young people into work to under-25s who have been claiming benefits for a year.

Eligible 18- to 24-year-olds will be “guaranteed” a fully funded, six-month job matched to their skills after 12 months on universal credit. The Liberal Democrats said the six-month offering was worth “very little” without a job at the end of it.

Before the publication of the report, Milburn said the government would have to be “candid with people”, that it would take 10 years for the benefits bill to come down, and investment would have to be made upfront.

Addressing critics calling for the benefits bill to be immediately slashed, the former health secretary told the BBC’s Sunday With Laura Kuenssberg programme: “There’s no such thing as a free lunch. If you are going to will the ends, you’ve got to will the means. I don’t think there’s a single person in this country who believes that it’s tolerable to have one million young people, aged 16 to 24, who are not in education, employment, or training.”

Pat McFadden acknowledged that Milburn’s review would have an “element of compulsion” for Neets and there would be people who would receive less in benefits than currently.

The work and pensions secretary said the UK had to become more like countries that had dealt with youth unemployment more successfully, such as the Netherlands, where the youth desk would “literally knock on your door” and offer options of training or work.

But he denied that Milburn was proposing a ban on young people claiming health-related benefits. “That’s not what he’s saying. He’s saying if you have a long-term disability, that means you can never work,” he said.

“You will actually get more than you will now. He’s saying that if you have extra costs, there will be a benefit you can apply to for extra costs. He’s also saying there should be a local fund for short-term needs, and for other people, he’s saying there should be more support to get into work.

Change was necessary, he added, because the number of young people claiming personal independence payments (Pip) had doubled since the start of the decade, while the number of young people on the health element of universal credit had increased by 80%.

Burham hit out at the Conservatives and Reform, who have called for deep and immediate cuts to welfare, with Kemi Badenoch vowing to slash the bill by £36.1bn by 2030 if the party wins the next general election. Under the plans 70% of child benefit disability-related claims linked to ADHD and “milder” behavioural disorders and learning disabilities would be cut, with Labour calling the proposals “a charter for human misery”.

The shadow work and pensions secretary, Helen Whately, acknowledged the plans could mean around half a million children losing disability-related payments.

“This is to help those children,” she told the BBC’s Sunday With Laura Kuenssberg, adding that under the plans, child mental health services would receive £1bn of funding. “The point of that funding is because there are children who are struggling. Let’s use this funding in the best possible way to support those children.”

Burnham accused past Conservative governments of taking “a deliberate decision to make young people bear the brunt” of austerity cuts. “What is the Tory solution now? To punish those young people once again,” he said.

“The crude cuts they are proposing … would simply compound the mistakes they made in government. They would drive children into poverty and increase levels of family homelessness even further, piling further pressure on councils, the NHS and other public services. This is not “reform”. It is a path to higher public spending and broken services.”