Passengers wait around in the South Terminal building at Gatwick Airport after drones flying illegally over the airfield forced the clossure of the airport, in Gatwick, Britain, December 20, 2018. REUTERS/Peter Nicholls - RC1A0D6EC370

A police helicopter flies over the closed runway at Gatwick Airport after drones flying illegally over the airfield forced the closure of the airport, in Gatwick, Britain, December 20, 2018.

Passengers wait around in the South Terminal building at Gatwick Airport after drones flying illegally over the airfield forced the closure of the airport, in Gatwick, Britain, December 20, 2018.

Stranded passengers wait at Gatwick Airport, Britain, December 20, 2018 in this picture obtained from social media.

Airport staff distribute chocolates and Christmas elf toys to waiting passengers in the South Terminal building at Gatwick Airport, after the airport reopened to flights following its forced closure because of drone activity, in Gatwick, Britain, December 21, 2018.

Passengers wait around in the South Terminal building at Gatwick Airport after drones flying illegally over the airfield forced the closure of the airport, in Gatwick, Britain, December 20, 2018.

Passengers wait around in the South Terminal building at Gatwick Airport after drones flying illegally over the airfield forced the closure of the airport, in Gatwick, Britain, December 20, 2018.

Passengers wait around in the South Terminal building at Gatwick Airport after drones flying illegally over the airfield forced the closure of the airport, in Gatwick, Britain, December 20, 2018.

An arrivals board in the South Terminal building at Gatwick Airport, after the airport reopened to flights following its forced closure because of drone activity, in Gatwick, Britain, December 21, 2018.

Aeroplanes taxi before and after taking-off and landing at Gatwick Airport, after the airport reopened to flights following its forced closure because of drone activity, in Gatwick, Britain, December 21, 2018.

Airport vehicles stand on the closed runway at Gatwick Airport after drones flying illegally over the airfield forced the closure of the airport, in Gatwick, Britain, December 20, 2018.

Passengers wait around in the South Terminal building at Gatwick Airport after drones flying illegally over the airfield forced the closure of the airport, in Gatwick, Britain, December 20, 2018.

Passengers wait around in the South Terminal building at Gatwick Airport after drones flying illegally over the airfield forced the closure of the airport, in Gatwick, Britain, December 20, 2018.

Passengers wait in the South Terminal building at Gatwick Airport, after the airport reopened to flights following its forced closure because of drone activity, in Gatwick, Britain, December 21, 2018.

Passengers wait around in the South Terminal building at Gatwick Airport after drones flying illegally over the airfield forced the closure of the airport, in Gatwick, Britain, December 20, 2018.

Passengers wait around in the South Terminal building at Gatwick Airport after drones flying illegally over the airfield forced the closure of the airport, in Gatwick, Britain, December 20, 2018.

Passengers wait around in the South Terminal building at Gatwick Airport after drones flying illegally over the airfield forced the closure of the airport, in Gatwick, Britain, December 20, 2018.

Passengers wait in the South Terminal building at Gatwick Airport, after the airport reopened to flights following its forced closure because of drone activity, in Gatwick, Britain, December 21, 2018.

Passengers wait around in the South Terminal building at Gatwick Airport after drones flying illegally over the airfield forced the clossure of the airport, in Gatwick, Britain, December 20, 2018.

A police vehicle stands on the closed runway at Gatwick Airport after drones flying illegally over the airfield forced the closure of the airport, in Gatwick, Britain, December 20, 2018.

Passengers wait around in the South Terminal building at Gatwick Airport after drones flying illegally over the airfield forced the closure of the airport, in Gatwick, Britain, December 20, 2018.

Stranded passengers are seen sleeping at Gatwick Airport, Britain, December 20, 2018 in this picture obtained from social media.

Passengers wait in the South Terminal building at Gatwick Airport, after the airport reopened to flights following its forced closure because of drone activity, in Gatwick, Britain, December 21, 2018.

Passengers wait around in the terminal building at Gatwick Airport after drones flying illegally over the airfield forced the clossure of the airport, in Gatwick, Britain, December 20, 2018.

Passengers wait around in the South Terminal building at Gatwick Airport after drones flying illegally over the airfield forced the closure of the airport, in Gatwick, Britain, December 20, 2018.

Stranded passengers look at the departures board at Gatwick Airport, Britain, December 20, 2018 in this picture obtained from social media.

Passengers wait in the queue for check-in in the South Terminal building at Gatwick Airport, after the airport reopened to flights following its forced closure because of drone activity, in Gatwick, Britain, December 21, 2018.

An airplane takes off at Gatwick Airport, after the airport reopened to flights following its forced closure because of drone activity, in Gatwick, Britain, December 21, 2018.