Foreign jihadists fleeing from Isil's shrinking caliphate are “hiding in plain sight” in migrant flows, the head of the Armed Forces has warned.

Air Chief Marshal Sir Stuart Peach said he was concerned about the global reach of Isil’s ideology and the prospect that internet radicalised copycat terrorists could pop up around the world.

Chief of the Defence Staff also said Britain had entered a new era of “state on state competition” with nations such as Russia and China.