Terrorists want to use the unmanned machines – available for as little as £100 on the high street – to drop explosives on large crowds at popular sporting and cultural gatherings. Defence chiefs fear they could launch a multi-drone attack carrying several bombs, even using airborne cameras to film the bloody carnage below for twisted propaganda videos. Senior MI5 figures believed that Isis has already tested how much plastic explosive the flying machines can carry, getting as far as experimenting with detonation devices.

A counter-terrorism source said: “Islamist plotters have been trying to launch a drone-borne bomb attack for some time, as these machines are getting more hi-tech every year. “They want the spectacular devastation of such a raid, which would cause murder and maiming in a crowd, while filming it for a sick video. “Isis is obsessed with re-creating the horror of 9/11 and believes this may be possible by launching a multi-drone attack on large numbers of people in a synchronised attack.” MORE