The drones are being controlled from close to the airfield, probably from a car or van that keeps moving or even continuously moving. It has been suggested that the batteries can be bypassed, not sure how you would do that in a drone flying a couple of miles away.
So they have to be close enough to change batteries, they control it with a smart phone app, probably one they have written or modified themselves, it is GPS guided and will fly back to the operator automatically wherever he is.
This is hard to stop because it uses mobile phone signals and there are thousands coming out of Gatwick
Probably not a Eco warrior just a hacker who wants to cause mayhem. He has had his fun and will vanish, until the next time.
It is being said that drones will bring great benefit to society - well, it will be a long time before the cost of this chaos is recouped, not to mention the prison drone issue.