A British intelligence chief has warned Russian spies could soon launch a fresh wave of drones at military HQs across the UK in a bid to cause mayhem - amid alarm over sightings worldwide. Last month saw a mysterious swarm of drones targeting three air bases used by the US Air Force, which triggered a scramble by British troops and police. The unmanned aerial vehicles - or UAVs - were seen hovering over RAF Lakenheath and RAF Mildenhall, in Suffolk, and RAF Feltwell in Norfolk, over several days, in a what defence sources described as a 'coordinated' operation.