Opposition politicians have called for tighter control of spending for the 2012 London Olympics after the BBC revealed the cost could rise to £9bn.
The cost estimates for London 2012 continue to rise
The new figure is four times that set out in the city's bid for the Games - up from an initial figure of £2.35bn.
The Conservatives and the Liberal Democrats have now urged the government to take more control of the cost.
The Department for Culture, Media and Sport (DCMS) said talks on the budget were still ongoing.
Costs have mounted since London won the right to host the games in July 2005.
In the wake of heavy criticism of the government's handling of the games, Culture Secretary Tessa Jowell admitted to parliament in November that the cost of the Games would rise by £900m - 40% - to £3.3bn.
But the BBC has found that construction alone will equal that figure.
In addition, the BBC has learned that a £2bn construction contingency fund will be set aside, with regeneration costs of £1.8bn and a £1bn VAT bill taking the total higher.
Shadow culture secretary Hugo Swire said the news of the rising costs was "staggering", and said Chancellor Gordon Brown should take responsibility, because he signed off the original budget.
"It is time we got a proper explanation from Gordon Brown on what has gone on and assurances as to what the government is doing to control the ever-increasing budget."
The Conservative chairman of the Commons Culture, Media and Sport committee, John Whittingdale, called on ministers to clarify costs "very soon".
He said the taxpayer should not be forced to write a "blank cheque".
The Tory MP for Maldon and East Chelmsford told the BBC's Today programme he feared the rising costs would have a "devastating" impact on other causes which relied on lottery funding.
"However much the overspend is, it's got to be found from somewhere, and at the moment the government appears to be suggesting that it should come out of the lottery," he said.
"Now the lottery is already having to contribute one and a half billion pounds which is going to mean a lot of the other good causes are going to suffer as a result."
And deputy leader of the Liberal Democrats Vincent Cable said the original estimate for the cost of the games was hopelessly inadequate.
"I think what is now going to have to happen is that the people who're organising the games are going to have go back to the original budget and see what they can do within that, because we just cannot have an open ended budget and people just signing cheques."
A spokesman for the DCMS said the BBC's cost estimate was "just the latest of many different figures to be quoted by the media in the last few months, claiming to be the cost of the 2012 games".
He said accurate figures would be announced later and denied claims government departments had clashed over the budget.
He said: "Discussions are going on across government to resolve outstanding issues and we will make an announcement about long-term budget figures when they have concluded.
Factors in costing
Along with the 60% contingency added to the construction cost, the rise in commodity prices, adjustments to transport figures to reflect 2012 prices and a revised estimate for inflation on construction costs have led to the spiralling Olympic bill.
In addition, the land in the east end of London chosen for the site needs decontamination and major remedial work before it can be fit for the games.
The Treasury has also decided that the Olympic Development Authority will have to pay VAT.
While VAT is in effect paid to the Treasury, the cash initially still has to be found before it is reclaimed.