A Commons committee has accused the government of "hampering" its scrutiny of the Universal Credit welfare policy.
The government had not always provided accurate and timely information on changes to the flagship benefit reform, the Work and Pensions Committee said.
It also warned the single benefit was being rolled out at a "snail's pace".
But the government said it had given "regular updates" to MPs and its plans were being implemented in a "slow, controlled and safe" fashion.
Universal Credit will replace six benefits, including jobseeker's allowance, income support, child tax credit and housing benefit, but its introduction throughout the country has been delayed.
In its latest report, the cross-party committee said there remained "worrying uncertainty" over the computer systems being developed to implement the reforms.
Problems with IT systems underpinning the project came to light in a National Audit Office report last September, but the government had known about them for at least 18 months, the MPs said.
"It is concerning that it took so long for the government to acknowledge openly that there were problems with Universal Credit IT," the report said.
"The government has hampered the committee's scrutiny of Universal Credit implementation by not providing accurate, timely and detailed information.
"It is not acceptable for the government only to provide information about major policy changes when forced to do so by the imminent prospect of being held to account in a public evidence session."
Dame Anne Begg, the Labour MP for Aberdeen South who chairs the committee, clashed with Work and Pensions Secretary Iain Duncan Smith when he last gave evidence to the committee earlier in February.
Speaking on Wednesday, Dame Anne said only 4,280 people were claiming Universal Credit at the end of last year out of 1.22 million jobseeker's allowance claimants, showing the scale of the challenge.
"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," she said.
"Given the excruciatingly slow pace of roll-out to date, it is hard to see how the most recent implementation timetable can be met."
Labour said the committee was right to draw attention to the "endless delays" in the project.
"Ministers promised one million people would be on the scheme by April 2014 but the latest figures show under 4,000 are," said shadow work and pension secretary Rachel Reeves.
"David Cameron must urgently get a grip of this crisis-hit policy before any more taxpayers money is wasted."
But a spokesman for the Department for 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."
The government's plans had been subject to significant scrutiny by parliamentary committees and government auditors, he added. "We do all we can to help these enquiries."