The government will not be able to meet its target for rolling out Universal Credit across the whole of the UK by October.
Universal Credit will roll six working-age benefits and tax credits into one monthly payment, and is meant to simplify the system.
The Department for Work and Pensions (DWP) has said that October will see six new jobcentres - Hammersmith, Rugby, Inverness, Harrogate, Bath and Shotton - pilot the system, and that the original target for the system to be fully operational in every area by 2017 would be met.
But ministers, including Chris Graying in 2011, had originally promised that the whole of the UK would implement Universal Credit by then, leading to accusations that the IT system is still not ready.
The DWP has been undertaking a review of the system and decided that it needs improvement, despite the fact that according to the department, it works.
Critics, including Labour's work and pensions spokesman Liam Byrne, said the delay showed Universal Credit had become "the biggest white elephant in Whitehall".
"David Cameron and Iain Duncan Smith have spent £420m of taxpayers' money to deliver Universal Credit in the grand total of just ten job centres - that's less than 1.5% of the nation's job centres," he said.
"Iain Duncan Smith must now ask himself if he is fit for purpose."
This is not the first time the IT system has been called in to question.
Last year a committtee of MPs called the timetable for rolling it out "very ambitious and leaves little opportunity for dealing with any problems which arise", while the government's Major Projects Authority has warned that Universal Credit was at serious risk of failure along with more that 30 other government schemes.
The basis of the scheme has also been criticised, with many claimants left poorer after its introduction.