The Government should call in the National Audit Office (NAO) to carry out a "warts-and-all" review of its flagship welfare programme, Labour has said.
The Opposition said if it won next year's election it would pause the troubled Universal Credit scheme for three months and ask the spending watchdog to carry out an investigation.
But shadow work and pensions secretary Rachel Reeves said ministers should take that action now to "finally get a grip" on the scheme.
She told BBC1's Sunday Politics: "We set up a Universal Credit rescue committee in the autumn of last year because we had seen, from the National Audit Office, from the Public Accounts Committee, report after report showing that this project is massively over budget and it is not going to be delivered according to the Government's timetable.
"So we have set up this committee because we believe in the principle of Universal Credit, we believe it's the right thing."
She said there was a lack of up-to-date information, partly because the Major Projects Authority excluded it from its latest review after it was "reset" by Work and Pensions Secretary Iain Duncan Smith.
Ms Reeves said: "This is a flagship Government programme, it's going to cost £12.8 billion to deliver and we don't know what sort of state it's in."
Setting out Labour's plan to pause the scheme, she said: "We would stop the build of the system for three months, call in the National Audit Office to do a warts-and-all report.
"The Government don't need to wait for the next general election, they could do that today, call in the National Audit Office, stop throwing good money after bad and finally get a grip of this incredibly important programme."
But Mr Duncan Smith defended the way the programme was being rolled out in a gradual way rather than in a "big bang", saying: " I didn't want to bring anybody on to Universal Credit only to find that they then suffered as a result."
Last week it was announced that the Universal Credit, which is replacing six means-tested benefits and tax credits, will be expanded across north-west England.
He told BBC Radio 5 Live's Pienaar's Politics: " The whole of the North West will essentially be using Universal Credit over the next few months and this process, complete with all the family types as well towards the end of the year and the beginning of next year."
Mr Duncan Smith said reports that the whole project could be scrapped were "complete nonsense".
He said: "We work very closely on a daily basis with the Treasury, with the Cabinet Office. It was me that instigated that process, which is unusual because that was not how things were done in the past.
"It was done when I decided that we had to reset this programme."
Some £ 40 million spent on software has had to be written off because it is of no further use, and a further £90 million has been spent on IT with a useful life of only five years.
But Mr Duncan Smith insisted the IT being developed would make sure the system was "remarkably safe and secure".
He said: "It is not two computer systems. What we decided to do, at the advice of the Cabinet Office, was to continue developing what we call the live service, which is the system we have got rolling out at the moment.
"Alongside that we are looking to complete that process at the end of it with what's called the digital change.
"The vast majority of all the systems that will be used in the digital process are hugely in the live service. So what we are developing in the live service will be used throughout in the digital system.
"What has happened in the last few years is, generally outside people have got to the view that there are event better ways to complete the way that people go online, and that's through the digital process."
He added: "They are two meshed together, they are running not as separate systems but they are in parallel and they will actually deliver a remarkably safe and secure system, that's my main priority."