The Government dismissed claims it had deliberately obstructed an inquiry into the botched roll out of their flagship Universal Credit reforms.
A spokesman for the Department of Work and Pensions said:
Universal Credit and its IT systems are very clearly working well, with claimants receiving the new benefit and moving into work.
We deliberately started in a slow, controlled and safe way, which the Committee itself has long recommended, so we can expand Universal Credit securely to more people.
Universal Credit is on track and we will start expanding it to other Jobcentres from this summer.
We have made our plans to roll out Universal Credit very clear with regular updates.
MPs have expressed scepticism about the Government's ability to deliver wide-ranging benefit reforms on time.
The Work and Pensions Select Committee said Iain Duncan-Smith's department had worked at "a snail's pace" and failed to be open and transparent with their investigation.
Whilst it is right to ensure that the system works properly before extending it, there is a difference between cautious progress and a snail's pace.
Given the excruciatingly slow pace of roll-out to date, it is hard to see how the most recent implementation timetable can be met.
Effective select committee scrutiny depends on the provision of accurate, timely and detailed information by government departments.
DWP has not always provided this to the committee in the case of Universal Credit.
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."