I spent the best part of four years working on the new Heathrow Terminal 2, during which time there were a few incidents that required either one or both runways to be closed, so I got to see a lot of this play out first hand. There was clearly a playbook, and things generally happened very quickly and smoothly when the need arose, although the knock-on effects would often last for the rest of the day, and sometimes even into the next day (the maintenance window at LHR is only a few hours each night). The overall disruption that results is, as the Gatwick video shows, pretty severe and spans a large geographical area, so closing a runway, or the entire airport is clearly a major decision with a LOT of knock-on implications. Especially so around London where the space available to hold aircraft is limited by the proximity of a number of other airfields (civillian and military).
That Gatwick was willing to shutdown their entire operation for several hours at a time because of a presumed sighting of a drone is certainly laudable from a safety perspective. However, from a practical one, especially given the mounting number of "sightings" without hard evidence steadily increasing, combined with incidents like the wrongful arrest, the distinct impression I got was a LOT of people, in multiple organizations, running around like headless chickens in full-on panic mode. If they'd planned for this kind of thing - and it wasn't the first time a drone has disrupted an airport - the plan certainly didn't survive contact with the "enemy", that might not even have existed in the first place.
