Using jammers is illegal without proper permits, I'd assume that government would authorize Heathrow to jam drones. The only illegal activity is by the person flying the drone whom they want to locate and arrest. If the jamming results in the drone crashing, well, that's not an issue - it would be also completely reasonable to directly destroy the drone by physically shooting it out of the air where it should not be.

Surely any drone pirate worth his/her salt would use a CDMA radio?

No, that's too high latency to control the drone reliably after GPS is jammed (and if it's not jammed, the drone will just return to you when it loses signal anyway).

Radio waves, traveling at the speed of light, have too much latency?

Oh you meant setting up a CDMA base station somewhere, faking a cell tower and controlling the drone that way? I misunderstood, that sounds like a practical and affordable solution that will surely escape detection and be better than a $50 handheld controller.

I wouldn't be so certain that setting up a fake cell tower would escape detection. You'd have people triangulating your position and preparing enormous fines as soon as you turned it on, well before controlling a drone with it.

Unless you were being sarcastic? It's hard to tell on the internet.

I was, yes. You're either using CDMA over the cell network so you can be far away, or you're using a $50 radio that has a 20 KM range itself.

No, I meant both the controller and drones radio use the CDMA modulation technique to transmit at power levels imperceptibly above the background noise levels. A listener would only hear white noise and would not even know the drone/controller are transmitting.

(This is after all what CDMA spread spectrum modulation was invented by Hedy Lamar for)

Absolutely nothing to do with the W-CDMA telephone system.

What's the transmission power for those? Current RC transmitters transmit at 10 mW or so.

Just above the noise floor of each frequency in the band at the time of transmission. Hence undetectable.