A probe into the Government's affordable house building plans raises serious doubts about whether all the homes can be delivered by the 2014/15.
Auditors said they were concerned that more than half of the planned homes are not due to be delivered until the final year of the programme.
They also raised concerns that nearly one fifth of contracts still needed to be signed and pointed out that some housing providers felt they may not be able to charge rents at the levels they originally agreed.
The report, which was published today, did declare the launch of the Affordable Homes Programme a success, with providers aiming to build some 80,000 homes for the £1.8 billion of government investment, compared to the initial target of 56,000.
Amyas Morse, head of the National Audit Office, said: "The Affordable Homes Programme has made a good start, with providers committing themselves to building some 24,000 more homes than originally expected.
"There are key risks, however, including the fact that more than half of the homes are planned for the final year, with no room for slippage.
"The final judgment on the success of the programme will depend on how well these risks can be managed between now and 2015."
Mike Leonard, director of the Modern Masonry Alliance, said: “The audit report has flushed out the harsh truth. We need growth and jobs now and yet the majority of the public rented housing that will deliver it is pushed back to 2015.
“This Government needs to stop playing with numbers and Get Britain Building now.
“Our industry is ready and willing to build 25,000 public rented homes which will turn around our economy creating growth, jobs and social inclusion.”
Under the AHP model, the Government pays less grant per home than under previous schemes - £20,000 compared with £60,000 under the previous National Affordable Housing Programme.
But housing providers are free to borrow more and can charge higher rents.
But even with this freedom to raise extra funding, the new scheme represents a reduction of 60% in average annual spending on affordable homes over the four years of the Programme from 2011-12 to 2014-15, when compared to the three years up to March 2011.
The NAO also said the programme increased providers’ financial exposure, both in securing bank financing for capital investment and over the cost of supporting both future and existing debt.
