The Government has been accused of "hampering" an inquiry which found tens of millions of pounds had been wasted on flagship Universal Credit reforms.
The Work and Pensions Select Committee said there remained "worrying uncertainty" about the computer system being used to usher in the new single payment for unemployed or low income families.
The committee suggested the Department for Work and Pensions (DWP) had not been cooperative during the investigation and urged them to be "clear and frank" about implications of delays.
Computer problems meant that £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, said the committee.
Universal Credit will replace six benefits, including jobseeker's allowance, income support, child tax credit and housing benefit, but a national roll out has been delayed.
In response to Cabinet Office minister Francis Maude's admission that the implementation of the Universal Credit system has been "pretty lamentable", the Department for Work and Pensions has told ITV News Iain Duncan Smith has "not shied away from any tough decisions" over the policy:
DWP spox says Iain Duncan Smith has not shied away from any tough decisions in terms of Universal Credit development and implementation.
Labour's shadow work and pension secretary Rachel Reeves has asked "when will the PM and IDS [Iain Duncan Smith] get a grip" on Universal Credit, after Cabinet Office minister Francis Maude admitted to ITV News that its implementation had been "pretty lamentable" so far:
Even cabinet ministers are now admitting Universal Credit is a shambles. When will PM and IDS get a grip? http://t.co/atKNnM5yU7
Work and Pensions Secretary Iain Duncan Smith has denied claims that his welfare reform programme is a "debacle".Read the full story ›
The Department for Work and Pensions has confirmed that £40.1 million had been written off on software and computing costs during the introduction of the new Universal Credit system.
Annual accounts will show £40.1m write-off for Universal Credit IT which includes the £34m we previously announced
Re discussion of £90m IT today - we will be using this while we continue to roll out UC over the next five years. Not a write-off.
The Work and Pensions Secretary Iain Duncan Smith has denied claims that his welfare reform programme is a "debacle".
Speaking in front of MPs today, Mr Duncan Smith admitted the introduction of the new system was running late, but revealed the IT problems that initially disrupted the programme were now fixed.
Work and Pensions Secretary Iain Duncan Smith has insisted his flagship welfare reforms remain on track, despite further delays to the programme.
Mr Duncan Smith disclosed last week that his 2017 target for the full introduction of Universal Credit is set to be missed - with around 700,000 claimants facing a longer wait.
Speaking ahead of his appearance before the Commons Work and Pensions Committee, he said the delay was to allow the most vulnerable claimants more time to adjust to the change.
"We could easily have tried to rush those people in but we have decided not to. I think it is only fair to give them longer," he told BBC Radio 4's Today programme.
"I do accept, of course, that this plan is different from the original plan."
Giving evidence alongside Iain Duncan Smith at the work and pensions select committee will be Howard Shiplee, the former London Olympics executive drafted in earlier this year to "reset" the Universal Credit programme amid growing concerns over delays and IT issues.
The Secretary of State may also be questioned about reports - which he denies - that he sought to have MPs pin blame for the failures on the DWP's chief civil servant Robert Devereux.
In his reply to the Autumn Statement, shadow chancellor Ed Balls taunted Mr Duncan Smith, commonly known as "IDS", over the reforms, suggesting it stood instead for "In Deep Shambles".
In written evidence to the committee, the DWP said it was "confident that it has taken, and continues to take, the right remedial steps to address past issues in the Universal Credit programme."
Shadow work and pensions secretary Rachel Reeves said the extent of the delay to the Government's introduction of Universal Credit was set out in data released by the Office for Budget Responsibility (OBR) alongside the Chancellor's Autumn Statement.
David Cameron and Iain Duncan Smith repeatedly promised to deliver their flagship policy 'on time and within budget'. That claim, and the credibility they staked on it, now lie in tatters.
For months on end the Government have tried to avoid answering questions about Universal Credit but these OBR figures tell the truth of how (they) have broken their promises on a spectacular scale.
They have been forced to admit that they have completely missed their targets and Universal Credit will not now be rolled out before the election. David Cameron and Iain Duncan Smith are presiding over a complete mess and it is taxpayers who are picking up the bill with at least one hundred million pounds of their money written off.