Gatwick has reopened after flights were grounded by drones over the airport, but police still do not know who is behind the disruption.
The first plane to take off in 36 hours left for Lapland at 6.33 on Friday morning, after the airport announced that the runway was open and flights would be arriving and departing.
However, delays and disruption will continue and those travelling have been advised to check with their airline before leaving for the airport.
Pilots’ union BALPA says it remains “extremely concerned” that flights have resumed while the threat of drones reappearing remains.
Gatwick’s Chief Operating Officer Chris Woodroofe said: “A number of mitigating measures in place provided by a number of government agencies and the military to ensure that I have the confidence to be able to reopen by airport.”
He would not elaborate on what the measures were.
Transport Minister Chris Grayling said police were pursuing a number of lines of inquiry in their search for who was behind the disruption, including whether it is “an individual with a grudge of some sort”.
“It is not a terror incident in the conventional sense, it is a disruption incident of a kind that we have not experienced in this country before [and] other countries haven’t experienced,” he said.
Asked by Sky News if the disruption was part of an environmental protest, Mr Grayling said it was “clearly one possibility” but added “we genuinely don’t yet know at this moment”.
More than a hundred thousand Christmas travellers were affected by the airport’s closure, in what was the biggest disruption for years.
Assistant Chief Constable Steve Barry told Sky News they are now in a better position to respond to the drones, the last of which was last seen just before 10pm last night.
“We’ve got measures in place now where if the drone appears in terms of physical response, in terms of a technical response, we should be in a much better position now to track and capture the drone.”
He said events “have been unprecedented in terms of what we have had to do, to mitigate the circumstances”.
He added that under the charge of endangering an airport the culprit could face life in prison.
Mr Grayling said “some serious steps” need to be taken around the protection of airports for drone incidents.
“There is no doubt that this poses a big challenge because there is no yet simple commercially off-the-shelf technology that can guarantee to dispose of, to prevent a drone from coming close to an airport,” he said.
Mr Grayling said there are some limited technologies being used in some airports, including Heathrow, but they are not “failsafe”.
The drones were first spotted on Wednesday evening.