G4S said chief operating officer David Taylor-Smith and global events director Ian Horseman Sewell had resigned following an internal review into the debacle which saw the firm admit just two weeks before the London Games began that it could not provide a promised 10,400 venue guards, forcing troops to step in and fill the shortfall.

"Whilst the CEO has ultimate responsibility for the company's performance, the review did not identify significant shortcomings in his performance or serious failings attributable to him in connection with the Olympic contract," G4S said in a statement on Friday.

The report said the contract problems were largely specific to the Olympics, with the company not planning sufficiently for the scale and complexity of what was needed.

Taylor-Smith was responsible for the contract and for ensuring it was delivered on budget and on time, while Sewell was the account director who told Reuters just before the Games that the company could have delivered two events of that scale at the same time.

However, Buckles, who has been with the world's biggest security group for 27 years, has been the face of the Olympic failure, taking to television and radio airwaves to apologize to the British public and twice being hauled in front of a Parliamentary Committee to explain what had happened.

G4S has largely prospered under Buckles, who has presided over a share price rise of some 76 percent since being elevated to group CEO in July 2005.

But investors have worried that the Olympics affair could jeopardize G4S's relationship with the government, a core customer, at a time when Britain wants to heavily involve the private sector in running public services.

Government deals account for over half of G4S's 1.8 billion pounds ($2.9 billion) British revenue and make up more than 20 percent of its pipeline of potential UK work, which includes prison management deals and electronic tagging contracts.

(Reporting by Rosalba O'Brien and Neil Maidment; Editing by Elaine Hardcastle)

• A Permanent Economic Emergency