Re: No gumption
Maybe the operators have indeed “armed the drone”.
That makes your proposed non-solution [“careful now”] much worse.
Options:
A) Marksman rifle shot. Risk - spent rifle bullet or drone carcass hits somebody. Risk level - density of people on ground, a few thousand x 0.1m2 per km2 => less than 1 in 1000. Consequence - a couple dead. Bad, but let’s see what option B has to offer.
B) Do nothing. Risk level - fairly high that this is either a serious attack in progress, or an initial probing for a larger attack if the culprits are not stopped. Probability surely at least 10%. Or even say I am paranoid, but not less than 1%. Consequence: loss of one or several airliners, each with hundreds of people on board.
Personally, I choose option A.
Gatwick have gone for B; now we just wait for more attacks, one of which may well succeed with a large number of deaths. Bad choice.