Gatwick remains vulnerable to a further drone attack after being crippled for 24 hours, with pilots voicing “extreme concern” after the airport re-opened.

The warning came from UK pilots after the runway came back into use early this morning to allow a limited number of flights to resume.

Pilots union Balpa said the information it had was that Gatwick was re-opened despite the rogue drone or drones remaining undiscovered.

“We understand that detection and tracking equipment has now been installed around the perimeter of Gatwick and the expectation is that if and when the drones re-appear, they will be detected and the airport will close again,” the association said today.

General secretary Brian Strutton added: “It is up to the relevant authorities to decide whether it is safe to re-open Gatwick given that the rogue drone is still around and may be expected to fly again.

“Balpa is not aware that any special advice has been given to pilots operating into or out of Gatwick and so we have this morning ensured that all our UK pilots have Balpa’s advice on what to do if they see a drone while flying.

“Balpa remains extremely concerned at the risk of a drone collision.

“It is possible that the rogue drones may go undetected around the perimeter or could obstruct the flight paths outside the immediate detection zone.

“Given this continuing threat we have this morning issued our advice to pilots about steps to be taken if a drone is sighted.”