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And though two systems were deployed - one British and the other Israeli - flights only resumed because they were able to accurately detect that the drone's position was not a threat to

air traffic or civilians. Bizarrely, while the UK purchased the Israeli-made Drone Dome system in August for £2.5million, health and safety concerns resulted in the Ministry of Defence not

authorising the additional purchase of its "hard kill" laser system, which would have targeted and destroyed the "unmanned aerial vehicle". It means the Israeli Rafael

system was armed only with detection and tracking technology. A second British-made system, used by the MoD against IS, does carry jamming technology which can both "cut the cord"

to the drone's operator and immobilise the motor over a safe site. But last night sources revealed that this was not used because it was not needed. "Once the UAV was targeted, it

was decided that its flight path did not present a danger and flights were resumed," said a source. "That changed briefly on Friday night, where flights were again suspended for an

hour." More than 1,000 flights were cancelled over a 36-hour period, disrupting 140,000 passengers in what former head of the British Army Gen Lord Dannatt last night branded "a

national embarrassment". Owners of drones weighing 250g or more must register with the Civil Aviation Authority. The craft must not be flown above 400ft or within one kilometre of

airports. Those breaking the law face a five-year prison sentence. But legislation still hampers the use of anti-drone technology near an airport, which may have accounted for the delay

before Sussex Police authorised military involvement.  "Put simply, the police had to bend the law at Gatwick, though changes to regulations are expected in the near future to

facilitate anti-UAV defence systems," a Whitehall source confirmed last night. Units from the RAF and Army were deployed using both the Israeli and British systems from rooftops.

However Britain's decision not buy Rafael's "effector" laser - which can destroy a drone up to 10km away - makes any operation to eliminate them much tougher.