Boris Johnson refuses to explain how Universal Credit claimants can make up lost £20-a-week

Tory MPs told to abstain in Commons vote, allowing Labour motion demanding cancellation of the cut to pass – but it is non-binding

Boris Johnson has refused to explain how Universal Credit claimants should recoup their looming £20-a-week cut in payments, as he branded criticism of the move “absurd”.

In fierce clashes in the Commons, the prime minister was challenged to set out how many hours of extra work will be needed – after a Cabinet minister wrongly claimed it is just 2.

But Mr Johnson declined to say whether the true figure is higher or lower – after experts concluded the answer is up to 9 – and instead criticised putting taxes “into benefits”.

Keir Starmer, speaking ahead of a Commons vote on the controversy, said a single parent on the minimum wage would have to find an extra 9 hours a week “just to get the money back that the prime minister has taken away from them”.

“Why is the prime minister choosing to take a tax system already loaded against working people and making it even more unfair?” the Labour leader demanded to know.

The £20-a-week cut – which will kick in next month – is predicted to plunge half million more people into poverty, including 200,000 children.

Labour staged a Commons vote, but Conservative MPs were told to abstain on the motion to cancel the cut, which meant it passed – but the vote has no impact, because it is non-binding.

Four Conservative MPs did rebel by voting with Labour: Peter Aldous, Neil Hudson, John Stevenson and William Wragg

Stephen Crabb, the former work and pensions secretary, criticised the “sudden, abrupt withdrawal” of the £20 uplift, which “is not the right way of doing welfare policy”.

On Monday, Thérèse Coffey, the work and pensions secretary, got her sums badly wrong when she said claimants should find more work because “£20 a week is about two hours’ extra work”.

It was quickly pointed out that Universal Credit is deliberately “tapered”, so a huge chunk of the payment is taken back as earnings rise.

The respected Resolution Foundation think-tank said claimants take home as little as £2.24 per for every hour worked on the national minimum wage of £8.91, after travel and childcare costs.

They would need to work an extra six hours a week to make up the £20 cut in support – rising to nine hours if they pay tax and National Insurance, it found.

Sir Keir said: “The truth is that these low-paid workers can’t work longer hours to get back the money the prime minister is cutting from them.”

“The reason is this: why would they have to work an extra nine hours, a full day every week, to get that £20 back – because of his broken tax system.

But Mr Johnson replied: “What I can tell him is that under this government, for the first time in decades, wages are rising.”

He added: “Of course, what they want to do is to continue to take money in taxation and put it into benefits. We don’t think that’s the right way. We want to encourage high wages and high skills.”