UK security giant G4S has revealed that the London 2012 Olympic Games cost the group £50m, after it failed to uphold its contract to provide a set number of security personnel for the event.

The group, which was contracted to supply 10,400 security guards to the 100 Olympic sites across the country, was unable to meet this target - forcing the UK government to draft in soldiers and police officers as cover.

The £50m losses are at the top end of analysts' predictions, and have dragged down G4S's profits by 60 percent. Its half-year pre-tax profits have fallen from £151m to £61m on the Olympic contract loss.

However, turnover increased by 5.9 percent to £3.bn, and, excluding the Olympic Games contract, sales rose by 5.8 percent.

G4S faced intense criticism after it failed to meet its £284m contract and the group's CEO Nick Buckles has profusely apologised since the event.

"We are deeply disappointed that we had significant issues with the London 2012 Olympics contract and are very grateful to the military and the police for their support in helping us to deliver a safe and secure games," said Buckles.

Before the start of the London Olympics, Buckles spoke at a hearing with the parliamentary committee in London and admitted his management of the London Olympics staffing scandal had embarrassed the British government and left the reputation of the world's biggest security firm in tatters.

Despite failing to meet the full demands of the contract, the group emphasised that it still delivered 83 percent of contracted shifts during the Olympics, and is confident that the Paralympic Games, which begin on 29 August, will be fully staffed.

However, the disappointment in not fulfilling the demands of its London 2012 Olympic contract will have a long-term effect on the company, as it now says it will not be bidding for the Fifa World Cup security contract in 2014.

G4S shares fell in early trading by over 2 percent as of 0704 GMT at 260.70p.