Olympic contractors who fail to deliver their obligations should be hunted down and forced to pay back money, Prime Minister David Cameron has said.

His comments came as ministers drafted in an extra 3,500 military personnel to protect London 2012 venues after private company G4S admitted it might not be able to provide enough guards.

"I'm absolutely clear that if companies don't deliver on their contract then they should be pursued for that money," he said.

Liberal Democrat MP Ian Swales, a member of the public accounts committee that has examined some G4S Olympic contracts, accused the company of "compounding a felony" by charging "colossal" fees for a "very poor service" when they should have given a "Rolls Royce service".

"We were really concerned because when the announcement of doubling of the number of security personnel was made we looked at the breakdown of the costs and we saw that the G4S contract was going up from £86 million to £284 million, which felt like a colossal amount of money."