David Cameron says seven terrorist plots have been thwarted in the UK this year alone. Mass casualty attacks, like those seen in Paris, are on the agenda too according to the head of MI5.
What is going on in the communities from which this largely "homegrown" threat has emerged? In an attempt to understand, Edward Stourton gathers a group of Muslim journalists with grassroots knowledge.
Producer: Sally Abrahams.
After the mass casualty attacks in Paris, could terrorists do the same in the UK?