Britain's security services may need greater powers of surveillance to monitor British citizens who have gone to join the fighting in Syria and Iraq, according to the former Conservative defence secretary Liam Fox.

As further details emerged about the latest young Britons to join Sunni insurgents, Fox said that the majority of people in the UK would accept that the level of the threat meant that officials would need greater powers to intercept the communications of extremists.

"The whole area of intercept needs to be looked at," he said. "We have got a real debate, and it is a genuine debate in a democracy, between the libertarians who say the state must not get too powerful and pretty much the rest of us who say the state must protect itself."