The Department for Education's budget for free schools is now at £1.5 billion, much higher than original estimates.

This is according to the National Audit Office (NAO) in its Establishing Free Schools report, which lists the going rate for setting up a new school, from the building process to filling teaching jobs, as £6.6 million.

In total, 174 schools have been opened as of September this year, educating 24,000 pupils, averaging at just under 115 students per facility.

Figures within the document suggest many of these free places are being taken up by middle class children. It found only 16 per cent of pupils were eligible for free school meals, typically based on family income, compared to 25 per cent in neighbouring schools. The average for all schools across England was 17 per cent.

It also found students were, on average, travelling over double the distance of those going to other local schools.

Overall, only three-quarters of spaces were filled in the first year of a new school. The NAO criticises schools opening in temporary accommodation, which the Department for Education spent at least £27 million doing, as these generally struggled to fill all positions.

Commenting on the report, chair of the Public Accounts Committee Margaret Hodge said: "While it is too early to judge the overall success of the programme, I am concerned about proper accountability for public money. A number of high profile cases have already surfaced, suggesting that monitoring systems remain inadequate.

"These cases highlight the urgent need for the Department [for Education] to reassess its oversight of fledgling schools, get a grip on underperformance and prevent the misuse of public money."

According to NAO's report, the government body originally underestimated how much was needed when it asked for £900 million in the 2010 Spending Review and, even then, it was only able to set £450 million aside.

It has since increased this to £1.5 billion, an eighth of its own total budget, through additional support from savings and the Treasury.

By March next year, the Department for Education will have spent £743 million.