Keith Vaz: Why MPs want to question G4S chief Nick Buckles

The chief executive of security firm G4S will go before MPs later to explain why his company was unable to provide the Olympics staff it promised.

Nick Buckles has already apologised after 3,500 extra troops had to be deployed to meet the firm's shortfall.

Chairman of the Home Affairs Select Committee, Keith Vaz, said the hearing was an attempt to find out all the facts.

''This is not the end, it's only the beginning,'' he said.