MI5 boss: UK faces 'more complex and ambitious plots'

The threat of a terror attack in the UK is increasing and the security services cannot hope to stop every plot, the head of MI5 has warned.

Speaking after the attack on the French magazine Charlie Hebdo, Andrew Parker said police and MI5 had "stopped three UK terrorist plots" in recent months.

The MI5 chief also revealed that the number of Britons who had travelled to Syria was now around 600.

Gordon Corera reports from the MI5 headquarters in London.