A group of MPs has labelled the government’s evaluation of the cost of hosting the Olympic Games as being “entirely unrealistic” and “wishful thinking”.

In its report into the costing of the 2012 Games, the Public Accounts Committee (PAC), a cross-party parliamentary body, said the Department of Culture, Media and Sport (DCMS) had ignored foreseeable major factors such as tax and security in its initial budget.

In its original budget in 2005, the government estimated that hosting the games would cost just over £4bn. Last year, however, it was forced to readjust the assessment and more than doubled the budget to £9.325bn.

In the report, PAC also casts doubt over the government’s legacy plans.

“Despite the £5.9bn increase in the public funding for the Games, the DCMS has not specified what will be delivered in return for this expenditure and the current budget cannot be reconciled to the commitments in the original bid,” it said.

The committee called for the government to publish a statement which clearly lists all legacy plans and how they will be delivered, in order to make the DCMS accountable for the Olympic programme.

Edward Leigh, conservative MP and chair of PAC, said: “It is now clear that the estimated cost at the time of the bid, just over £4bn, was entirely unrealistic.”