Iain Duncan Smith, the work and pensions secretary, is being urged to clarify whether he is on course to start implementing the biggest postwar change in welfare payment next April amid signs the cost is escalating.
Labour is due to stage a debate on universal credit in the Commons on Tuesday when it plans to challenge Duncan Smith on whether he should defer the implementation timetable, and on whether key decisions, including the direct payment of housing benefit to claimants and the future of women's refuges, had been settled.
Evidence from councils, charities and welfare groups to the Commons select committee inquiry into universal credit reveals growing concern about details of the vast project, including its impact on vulnerable groups, such as those that do not use the internet, or those in women's refuges.
Refuge, the country's largest single provider of specialist domestic violence services has claimed universal credit could see the closure of all 297 of its refuges.
Cameron offered the work and pensions secretary the chance to shift post in the reshuffle, apparently reflecting Treasury nerves at the grip the Department of Work and Pensions has on Universal Credit.
Shadow work and pensions secretary Liam Byrne said: "The problems for universal credit are mounting up, yet much of the project remains shrouded in secrecy.
"Ministers must now come clean, make public all of their plans for universal credit – including the secret business case – and do everything they can to address the serious flaws that have been exposed."
The Centre for Social Justice, the thinktank established by Duncan Smith in opposition sprung to his defence. A spokesperson said that while a debate around the implementation of universal credit is important, many of the concerns raised by this collation of responses are out of date or already being addressed by ministers.
"A number of pilots will be run in the coming months to work through precisely some of the legitimate implementation points raised – we have all the evidence we need to get this right," the spokesperson added.
