Building schools programme over budget by billions

The report says costs for the secondary school rebuilding and refurbishment project have spiralled to between £52bn and £55bn, around £10bn more than was originally estimated.

Reasons for the price hike include unexpected building cost rises and higher than expected costs in setting up Local Education Partnerships, the public and private sector joint bodies that manage local projects.

The NAO also found that the Department for Children, Schools and Families, and Partnerships for Schools, the body set up to manage the project nationally, were "too optimistic" in their initial claims that 200 schools could be built by the end of 2008.

Just 42 were completed in 2008, with a further 54 due to open next year and 121 the year after.

The target is for work on all 3,500 secondary schools to be completed or well underway by 2020. The NAO says that 250 schools will need to be built a year to achieve this and warns that it is not yet known how the current financial crisis will affect this.

Schools minister Jim Knight admitted that, "there was an over optimism in terms of what could be done," but remained confident that the economic crisis would not affect building work.

Partnership for Schools chief executive Tim Byles added that six banks that withdrew their support for the project at the end of last year due to the squeeze on lending have signalled their intention to return.

The Conservative's shadow children's secretary Michael Gove has branded the government's handling of the project as "shambolic".