Labour looks less likely to meet its manifesto pledge to equalise the minimum wage for younger workers before the next election, after the chancellor failed to guarantee the rise would happen within that timeframe.

John Healey said on Sunday his party was "prepared to take hard decisions about the priorities in government", including possible spending cuts.

His comments came as a former adviser to Andy Burnham, the economist Andy Haldane, warned that UK public finances were in a perilous state and the government was "on a precipice" of Liz Truss-style meltdown. Government sources expressed anger at the comments, saying the markets had responded positively to the budget.

Healey said in interviews on Sunday that he wanted to take the minimum wage increase at a slower pace for younger workers. He said the government was still committed to the increase but failed to spell out when it would be achieved.

In the budget, a rise in the minimum wage to £13.21 per hour was handed to adults, alongside a rise to £11.27 for under-21s. A larger rise for younger workers would have been needed to move towards equalisation.

Speaking on the BBC's Sunday with Laura Kuenssberg programme, Healey said he would take equalising the rates "one step at a time", amid fears a rise could exacerbate youth unemployment.

Labour's 2024 manifesto committed to closing the gap on pay for 18- to 20-year-olds, but last week's budget brought in a blanket increase of 3.9%.

Some senior MPs – including the housing secretary, Angela Rayner, while she was out of government – have previously expressed concern at the slow pace of the equalisation. In June, Rayner warned the government it must deliver on the promise.

Healey said the government was still committed to the eventual equalisation. "I legislated as a new MP for the national minimum wage when we first brought it in [in 1998], and so we're going to have to continue to make those trade-offs between jobs and wages," Healey said. But he denied Labour would break its manifesto commitment.

"There's no question about whether or if. It's a question of when. It's a question of how fast. And I want to make sure that we can look hard at those trade-offs that inevitably are there between jobs and wages.

"I want to take business, I want to take trade unions with me, and with the government, because together we have to get into what at the moment is a moral shame on this nation, a million youngsters written off, without any prospect of being helped into work and making a contribution to this country for the future."

Healey also told the BBC he was prepared to keep the spending cuts – some more than 2% year-on-year – planned for before the next election in the last spending review.

Some thinktanks including the Institute for Fiscal Studies have criticised how the government's deficit reduction plans seem predicated on making unpopular cuts that are unlikely to be enacted at a crucial electoral moment.

"We will carry that through to the 10-year plan and the spending review next year," Healey said. "But in the budget I also set out the ways that we're preparing and the work we've got under way to prepare for those spending review decisions."

But Haldane, the former Bank of England economist who advised Burnham in the summer before he became prime minister, said that was a "fierce urgency" to get spending and borrowing in better shape. "On the public finances, let's be very clear, we are on a precipice on that front, right? The risk of something untoward happening in public debt markets is very great.

He said that included "the sort of blowout and borrowing costs we saw under Liz Truss' mini budget but with more added on on top."

The comments have infuriated some ministers and aides, especially given Haldane's early connection to Burnham. One government source called the comments "genuinely irresponsible - he's going around talking Britain down, claiming to speak for the markets while saying the opposite of the published views of true market participants and analysts."

Gilt yields have fallen since the Budget and are on course for the biggest monthly decline since May, an indicator that markets are broadly unfazed by chancellor's actions, though the public finances remain precarious. Most analyses from investment strategists like Citigroup, L&G and Bloomberg suggest there is little to alarm the markets in the Budget.

Speaking on GB News on Sunday, the chief secretary to the Treasury, Emma Reynolds, said the government would not make "crude cuts" to welfare to balance the books –, because of the costs that would incur elsewhere.

"We will set out proposals in the new year, and then we will legislate to bring the welfare bill down in a fair and sustainable way, and according to our values as a Labour government. I know that other parties, such as the Conservatives and Reform, claim that they can do crude cuts to welfare," she said.

"The Conservative government didn't manage to do crude cuts because they know full well that if you push people into crisis, then you end up pushing costs into a different part of the public sector. So that's not the right way to do it because, frankly, this isn't realistic."