More than 20,000 G4S guards have been accredited to provide security for the Olympics but the firm is unable to get them to turn up at venues, it has emerged.

Up to 3,500 extra troops will be needed for security duties during the Olympics amid fears that private firm G4S will not be able to meet the needs, the British Defence Secretary will say today.

The US is reportedly preparing to send in 500 FBI agents to the London Olympics next year, following concerns about existing security arrangements for their athletes.

Briatin's Notting Hill Carnival was getting underway today, with millions of visitors expected at Europe’s largest street party.