Parliament's spending watchdog has warned that without strong risk management the London 2012 Olympic games risk delivery failure.
The National Audit Office's first report on the preparations for London 2012 identifies six main risk areas which may impact on the games.
According to the NAO the Games require effective budget management, co-ordination of the many organisations involved, an immovable deadline and a clear idea of a lasting legacy.
The auditors warn that a final agreed budget is necessary to ensure success of the programme.
Cost estimates for the Olympic park have risen by at least £900m since the time of the bid.
NAO chief Sir John Bourn said: "Finalising the budget should be a priority to allow the Olympic programme to move forward with greater confidence and certainty."
Opposition parties seized on the NAO findings to back their concerns about the financing of the Games.
Shadow Olympics minister Hugh Robertson said: "It is entirely the government's fault that the bid budget was so incompetently drawn up and it is their mismanagement of the inevitable aftermath that is doing so much damage to the Olympic process."
And Don Foster, Liberal Democrat sports spokesman, called for a clear budget to keep costs of the Games down.
"It's clear that the Lottery should not be treated as a Treasury slush fund to fill the current funding gap. Nor should Londoners face another raid on their council taxes," he said.
