Call me old fashioned but what if they decided to fly more than one 172, 152, pa28 at once.... then of course there are those numerous aircraft that are close to London, one would have thought the Missile defences would have been better forming a "ring of steel" around the perifery London, but no doubt our capabilities these days would have amounted more to a collander than a shield.
Suprised we can afford a CHAG these days let alone a RHAG