A computer glitch is partly to blame for a shortfall in security staff for the London 2012 Olympic Games.
Last week, security giant G4S admitted it would not be able to deliver the some 10,000 security staff it had been contracted to provide for the Games, resulting in about 3,500 military personnel being drafted in to make up the numbers.
Nick Buckles, chief executive of G4S, told the Home Affairs Select Committee on Tuesday the shortfall is "partly down to the fact our scheduling system hasn't effectively worked to roster the staff".
The software manages the rostering pipeline for applicants to be G4S security staff at the Games, he said, providing weekly reports on applicant processing. It is the same system that the firm uses to handle the deployment of security staff at sporting events every weekend, the committee of MPs heard.
Buckles said he had been made aware of the shortfall and the problems with the scheduling system on 3 July, but initially thought they could be resolved.
"We were still confident early on that we were going to produce the numbers. But the more and more we dug into the data, looked at the process and the scheduling day by day we started to realise that the pipeline and the people we thought we were going to be able to deliver, we couldn't," he said.
On Wednesday, 11 July, Buckles told government officials at an Olympic Security Board meeting that G4S wouldn't be able to provide the necessary security staff for the Games.
G4S will meet the cost of deploying military personnel to meet the security shortfall, as well as incurring other charges, which are expected to total £50m.
Buckles told the committee that he was "very sorry" for what had happened.