The UK’s armed forces are on standby to provide an additional 3,500 troops to help with security at the 2012 London Olympics, the BBC has learned.It comes amid fears that private contractor G4S would not be able to provide enough trained staff in time.The armed forces were already providing some 13,500 personnel – this could now reach 17,000, meaning summer leave for some troops will likely be cancelled.G4S said it had “some issues in relation to workforce supply”.G4S is being paid £300m to guard the Games, but the BBC understands it has not been able to guarantee it can supply the 10,000 guards it has been contracted to deliver.’No impact on security’A G4S spokeswoman said the company had accepted “that the government has decided to overlay additional resources.”She added: “This has been an unprecedented and very complex security recruitment, training and deployment exercise which has been carried out to a tight timescale.”We have encountered some issues in relation to workforce supply and scheduling over the last couple of weeks, but are resolving these every day and remain committed to providing a security workforce for the start of the London 2012 Games more