This has been going on since about 21:00 last night according to the BBC
"The shutdown started just after 21:00 on Wednesday when two drones were spotted being flown over the airfield. The runway was briefly reopened at about 03:01, the airport said, but forced to close again about 45 minutes later amid "a further sighting of drones".
In my view it is either not a drone but some other UFO or somebody is doing it on purpose to disrupt the airport as people do not normally fly in the dead of night.
There is a phone video on YouTube
That appears to show a light in the sky that is moving but it is difficult to judge how far away it is. I would have thought that a heat seeking camera would have been able to pick it up and lead Police to the pilot when they land to change batteries. Time MAY tell what really happened.