The Government has been accused of hampering an inquiry by MPs into the new Universal Credit benefit system, which found that tens of millions of pounds had been wasted.
The Work and Pensions Select Committee said there was worrying uncertainty over the computer system used to bring in the single payment for people looking for work or on a low income.
Universal Credit will replace six benefits, including jobseeker's allowance, income support, child tax credit and housing benefit. A UK roll-out has been delayed.
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The committee said the Department for Work and Pensions (DWP) needed to be clear about the implications of the delays and called for revised estimates of costs.
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 £90m has been spent on IT with a useful life of only five years, said the committee.
The IT problems were only revealed by a National Audit Office report last September, but the Government had known about them for at least 18 months, said the MPs.
"The Government has hampered the committee's scrutiny of UC implementation by not providing accurate, timely and detailed information," said the report.
Committee chairwoman Anne Begg MP said the lack of transparency was unnaceptable, adding: "We expect to have access to the information we need to scrutinise [the Universal Credit system] effectively.