Firms who fail to deliver on their contracts should be pursued for the money, the Prime Minister has said following the Olympic security row.

Ministers were forced to draft 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.

David Cameron's comments came as an MP accused G4S of "compounding a felony" by charging "colossal" fees for a "very poor service". Mr Cameron said: "I'm absolutely clear that if companies don't deliver on their contract then they should be pursued for that money."

He added: "I think we should be raising our sights, and thinking of the incredible inspiration that these Games are going to bring. The facilities are built, the country is ready, we are in really good shape."

But Ian Swales, a member of the public accounts committee that has examined some G4S Olympic contracts, said the firm should have provided a "Rolls Royce service" after hiking up its charges by £198 million.

The Liberal Democrat said MPs had raised concerns about what appeared to be massive profit margins on the contract after fees were increased when the need for extra staff grew. "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," he told BBC Radio 4's World at One.

He said the programme management costs, which cover training and recruitment, went up from £7 million to £60 million, while operational costs increased from £3 million to £65 million.

G4S was initially contracted by Games organiser Locog in 2010 to provide 2,000 security staff for £86 million, but that figure has since risen to 10,400 personnel in a contract now worth £284 million. G4S chief executive Nick Buckles and G4S global events specialist Ian Horseman-Sewell will give evidence to MPs on the Commons Home Affairs Select Committee on Tuesday, a spokesman for the committee said.

The chairman of the Commons Public Accounts Committee Margaret Hodge said they would be summoning G4S, Locog, the Home Office and the Department for Culture, Media and Sport to give evidence when Parliament returns in September. She said it was imperative that there was "total transparency" when public money was involved.

"What the National Audit Office has said to me is that it is unlikely that we will be able to claw back for the taxpayer money spent on overheads - that is where the big money has gone," she told BBC Radio 4's PM programme. "What none of us know is how that contract was designed, whether there was a penalty clause in it. Clearly we have to pursue that point. Where public money is being used, hiding behind commercial confidentiality is simply not good enough."