On July 2nd, 2017, Gatwick Airport in the UK was forced to suspend its runways for a total of 14 minutes because a drone was flown in restricted airspace. This 2-minute visualization released by NATS shows the chaos that ensued.
An approaching aircraft reported a sighting of a drone in the early evening and air traffic controllers took the decision to suspend the runways while the report was being investigated. The risk of a potentially catastrophic collision is very real.
The video tracks the movements of different planes that were trying to land in and pass by Gatwick at the time: