The ten memos - which ministers were forced to release by Parliament - reveal Universal Credit "was on the brink of complete failure” by 2013, the Commons Work and Pensions Committee said.
Despite being brought “back from the brink” and delayed nine times the benefit still costs £963 per claim, almost four times the target set to achieve by May next year.
Ministers' central boast that UC helps people into work is "highly uncertain” because the estimate relies only on single, childless, unemployed claimants, the MPs said.
And ministers are slammed for not having produced a full business case for UC even now, eight years after it launched.
Committee chairman Frank Field said: "They have produced no evidence to back up the key, central economic assumption of the biggest reform to our welfare system in 50 years.
"William Beveridge will be rolling in his grave.”
Labour used a Commons motion last month to force the government to hand over progress reviews by the Infrastructure and Projects Authority (IPA), spanning 2012 to 2017.
Not a single report gave UC a “green” rating, a clean bill of health.
Two in 2013 gave it the worst rating of “red”, which means “successful delivery appears to be unachievable”.
The others were “amber-red” or, in the case of the most recent three, “amber”. This means there are "significant issues" but they can be resolved if addressed promptly.The full reports remain secret but were summarised and quoted selectively for the first time in the MPs' report.
An information tribunal will hear arguments for releasing them to the public in April.
One report in March 2017 found at least one Jobcentre had not made a single decision on a claim in 25 days.Another in October 2015 warned there was a “risk” in moving claimants from housing benefit onto UC - almost two years before the issue exploded into a political row.
The same report warned the programme was "not without significant challenge or risk” and there was “no Plan B”.
The committee of MPs today said “many millions of pounds of public money were wasted” on UC in its early stages and declared: "By 2013, the UC programme was on the brink of complete failure.
"It is to the Department’s credit that it has brought it back from that brink.
"UC continues, however, to face major challenges.”The committee said research in September 2017 showed people on UC were four percentage points more likely than those on Jobseekers' Allowance to have been in work at some point six months after first claiming.
But the analysis, the committee said, "only covered single, unemployed claimants without dependent children.
"It quite possible that the employment impact of UC for people with more complex circumstances, who may face greater barriers to work, will be different." Shadow Work and Pensions Secretary Debbie Abrahams said: “This report proves once again that Universal Credit is not fit for purpose.
"It is completely unacceptable that the Government has not provided any evidence to back up their repeated assertion that Universal Credit will help people into work, a key principle of the programme."
A Department for Work and Pensions spokesman said: “UC claimants are moving into work faster and staying in work longer. We have announced £1.5bn extra
support for people moving onto UC and the IPA has supported our recent expansion of the programme.” What is Universal Credit?
A single system replacing six benefits: Child and Working Tax Credits, Housing Benefits, Income Support, Jobseekers’ Allowance, and Employment and Support Allowance.
It was launched in 2013 as the pet project of Tory Iain Duncan Smith supposedly to make work pay.
Who claims it?
Low earners, those out of work and the sick or disabled. Already 610,000 people are on UC - 8% of benefit claimants.
It is being rolled out to individual Jobcentres including 52 in October 2017.
What are the problems?
Debt-ridden claimants must wait six weeks (five from early 2018) for their first payment, with 19% waiting longer than that and 4% waiting ten weeks in late 2017.
Research also suggests overall, UC leaves many working families worse off than the old system.
That is because payments taper away at 63p for every £1 claimants earn.
The timetable has also been put back nine times since 2013 after a string of glitches and will only be fully complete in late 2022.