The suggestion is that the airports were under major terrorism threat, which is why the army was involved. They didn't say this to avoid spooking the public, and having a whole lot of people cancel their flights and holidays (plus it would have been major fuel for the Yellow Vests).
The yellow vests, as in the protests in France? What's that got to do with drones in the UK???
Here's a video of some people blocking a bridge, causing delay to an ambo: https://twitter.com/LeaveEUOfficial/status/10735588338789621...