Britain is facing an "unprecedented" threat from hundreds of battle-hardened jihadists who have been trained in Asia, Africa and the Middle East, according to MI5, the domestic counter-intelligence and security agency. It warns that are now more Britons trained in terrorism than at any point in recent memory.
More than 700 Britons are believed to have travelled to Syria and Iraq, according to British authorities. Over half of these Britons are thought to have since returned home, where they pose a significant threat to national security.
Britain's terrorism threat alert is at the second-highest level of "severe," meaning an attack is "highly likely."