Former work and pensions secretary Iain Duncan Smith has called on Prime Minister Theresa May to scrap £3.4 billion of cuts to Universal Credit.
Mr Duncan Smith said the move would help people back into work.
The Centre for Social Justice (CSJ), a think tank chaired by the former minister, released a report in which it says three million claimants of Universal Credit will be £1,000 a year poorer by the time the scheme has fully replaced working tax credits in 2022.
In 2015, cuts to the Universal Credit “work allowance” were announced - reducing the amount people could earn before benefit payments were withdrawn.
Just 25 per cent of spending to increase the income personal tax allowance reaches those needing it most, Mr Duncan Smith said.
“One of the key elements as you cross into work, the work allowances, those were all reduced. The problem with that is it means it is more difficult to get people into work and keep them in work.”