London: The leader of a parliamentary watchdog committee said on Friday she was "staggered" that organisers of this year's Olympics had managed to so dramatically underestimate the number of security guards needed to admit spectators into venues.

It is the second time this week organisers have been sharply rebuked by lawmakers. On Wednesday, London politicians accused the body responsible for staging the Games, LOCOG, of being "obsessed with secrecy" over its ticketing process.

Last December, the government announced the number of venue security guards needed as part of Britain's biggest peacetime security operation had risen to 23,700, from 10,000, with a doubling in cost to 553 million pounds.

LOCOG and the Interior Ministry said detailed security planning had only been possible once the venues had been built and competition schedules put in place.

But public finance watchdog, the Public Accounts Committee, said it was "particularly concerned about the significant increases in the security bill" which had eaten into the 9.3 billion pound overall Olympic budget.

"It is staggering that the original estimates were so wrong," said Margaret Hodge, chairwoman of the committee.

"The increase in the overall cost of venue security is the main reason why the public sector funding package is now so finely balanced," she added.

She also questioned whether LOCOG had secured the best deal during renegotiations with its security contractor.

"LOCOG has had to renegotiate its contract with G4S for venue security from a weak negotiating position and there is a big question mark over whether it secured a good deal for the taxpayer," she said. "There is no evidence the government has secured any price advantage."

The committee said the Olympic kitty could be left with just 100 million pounds or more once potential risks had been taken into account.

It also warned that LOCOG's budget, which is largely raised through the private sector via sponsorship, merchandising and tickets as well as contributions from the International Olympic Committee, was also under pressure.

LOCOG still needs 200 million pounds to reach its 2.2 billion pound target, though it expects 130 million pounds to come from remaining ticket sales, the report said.

However, it will only have five million pounds of headroom after risks are accounted for, and the government would have to guarantee any financial shortfall, the report added.

Taxpayers have already stumped up 867 million pounds, including a doubling of funds for the opening and closing ceremonies.

The committee also calculated that when other costs, outside the public funding package, were included, such as 766 million pounds for the purchase of the Olympic Park land and at least 826 million pounds for the legacy programme, the full cost to the public purse was nearer 11 billion pounds than 9.3 billion.

The government disputed the committee's figures, saying it still had over 500 million pounds of uncommitted contingency.

"We do not recognise the figure of 11 billion pounds," a spokesman added.

"The cost of purchasing the Olympic Park land will ultimately come back to the public purse through the resale of the land after the Games and was therefore not included (in the 9.3 billion pounds).

"Funding for the legacy programmes, that the PAC refer to, comes from existing business-as-usual budgets and we have been clear about this. These are for projects designed to capitalise on hosting London 2012 but are not an additional Olympic cost."