Claims that a flagship intervention project had turned around the lives of 99% of England’s most troubled families were misleading, a Commons committee has said.

The government also overstated the financial benefits of the scheme when it claimed it had saved taxpayers £1.2bn, MPs found.

They attacked the Department for Communities and Local Government (DCLG) for “unacceptable” delays and “obfuscation” in publishing an evaluation of the troubled families programme.

Rewarding local authorities that carried out the programme encouraged “perverse” behaviour, with some families pushed through the scheme too quickly, the public accounts committee (PAC) also found.

MPs called for the government to review the payment-by-results system for the programme to stop councils trying to speed families through the system. Local authorities claimed reward payments for 116,654 families out of the maximum 117,910 for which they could claim in the first phase, the report said.

MPs said the government had failed to prove the effectiveness of the initiative, which was launched by David Cameron in the wake of the 2011 riots to turn around the lives of 120,000 families in England by 2015 and later extended to help an additional 400,000 families.

It follows the release of research in October by the National Institute of Economic and Social Research (NIESR), which had been commissioned to carry out an official national study, that found the scheme had “no significant impact”.

Dawes (permanent secretary at the Department for Communities and Local Government) said that while the payment-by-results method had “galvanised” changes in the way services were delivered, officials were exploring other ways of financing the scheme in future.

MPs challenged officials as to why the evaluation was slipped out without fanfare at 6.15pm on Monday evening, more than a year later than its original publication date.

The committee’s chair, Meg Hillier, demanded to know if the report, which had delivered a devastating critique of one of the government’s top policy priorities, had been delayed as a way of suppressing its findings. She asked: “Who are you protecting in all of this? Are you protecting your department, your minister?”

Dawes denied the report had been buried and blamed some of the delays on problems with some of the data analysis carried out by members of the consortium of independent evaluators that produced the reports.

Casey (Former Head of the Programme) criticised individuals who had been involved in the evaluation and who made strong criticisms of the programme earlier this week, believed to be a reference to the economist Jonathan Portes, who accused ministers in an article in the Guardian of having misrepresented the troubled families data

Casey said: “I think that lots of comment made by those closely involved in the evaluation who have been leading in the press in the past few days has been unedifying.”

Ministers have quietly buried a report which concluded that one of the government’s flagship policies had “no discernible” impact on the problems of unemployment, truancy or criminality that it was supposed to address.

BBC 2’s Newsnight programme has seen the unpublished evaluation of the Troubled Families initiative that was launched in a blaze of publicity after the 2011 riots.

David Cameron promise to put ”rocket boosters” under Whitehall’s plans to aid troubled families, and forecast that by the time of the 2015 election it would “turn around” 120,000 households. In December 2011, he added: “Some in the press might call them ‘neighbours from hell’. Whatever you call them, we’ve known for years that a relatively small number of families are the source of a large proportion of the problems in society.”

Local authorities were given targets for the number of families they should sign up for the scheme, and a payment of £3,200 per family. Each family would be assigned a key worker who would be “assertive” and “challenging” in helping the family to get to grips with life.

Ministers hailed the results as a success. In March 2015, the then Communities Secretary Eric Pickles announced that the programme had had a “life changing impact” on 105,671 of the “hardest to help” families, saving taxpayers an estimated £1.2 billion in welfare and other costs

The programme was considered so effective that it was extended in June 2013 to take in another 400,000 families, at an additional cost of £900 million.

However, the definition of when a family had been “turned around” was vague enough for councils to report a 100 per cent success rate. When a consortium of analysts led by a consultancy called Ecorys had been commissioned to study the effectiveness of the programme, it appeared that being “turned around” may have meant very little in reality.

The consortium analysed data from 56 local authorities covering the first 18 months of the programme. According to the BBC, their report – submitted last autumn but never published – concluded: “The lack of obvious effect from the programme across a range of outcomes indicates that the programme did not have a measurable impact on families within the time-frame over which it was possible to observe its effects.”

Their analysis found “no discernible impact on the percentage of adults claiming out-of-work benefits” and “no obvious impact on the likelihood that adults were employed” 12 or 18 months after starting on the programme, and that the programme “did not have any discernible impact on adult offending” seven to 18 months after the family was booked into the programme.