2012 security costs break the billion-pound barrier

Fears that Games may exceed £9.3bn budget as estimate of personnel needed doubles

The cost of securing next year's Olympic venues and the cost of the opening and closing ceremonies were revealed to have doubled yesterday, as the Government was warned that the final cost of the London Games may exceed the £9.3bn budget.

A report by the National Audit Office cautioned that "there is real risk" more money will be needed to fund the Games. On the same day, the budget for venue security increased by £271m on the back of a dramatic revision in the required number of security personnel. An original estimate of 10,000 guards by London 2012 organisers has proved woefully inadequate.

Instead, 23,700 will be required to secure more than 100 venues at the Olympic Park and around the country. That takes the cost of venue security to £553m – up from last year's estimate of £282m – and brings the total cost of security, including £475m for "policing and wider security", to over £1bn.

The report says the Olympics remain on course, but there is little room to manoeuvre. Amyas Morse, the auditor general, said: "Not everything is rosy. The Government is confident that there is money available to meet known risks, but the likelihood that the Games can still be funded within the existing funding package is so finely balanced that there is a real risk more money will be needed."

Hugh Robertson, the Olympics minister, said the increased security was in part due to the "fluent security situation" and that it was only possible to settle on a figure for the number of personnel once the competition schedule had been settled and the venues had been completed.

"You can say this looks like a huge increase in the security budget or you can say this is what is needed to provide a safe and secure Games. The first responsibility of government is the safety of its citizens," he said.

It was also revealed yesterday that the Government will hand over £41m of public money to Locog to go towards opening ceremonies for both the Olympics and Paralympics.

Locog's budget is believed to have been £40bn but David Cameron, Mr Robertson and Jeremy Hunt, the Culture Secretary, want to ensure the opening ceremony in particular is a global "showcase" for the UK.