Olympics troops announcement due

Details of an additional 3,500 troops expected to be provided to help with 2012 London Olympics security are set to be announced by ministers later.

It comes after it emerged that UK armed forces are on standby to provide more troops in addition to 13,500 already agreed amid fears private contractor G4S may not have enough trained staff.

G4S said it had "some issues in relation to workforce supply".

Gordon Corera reports.