Starstreak was deployed during the Olympics to the top of small buildings in London. As it is a 'hittile' (ie. No big warhead) then it was deemed acceptable to fire it in a densely populated area if it was needed. However, Heathrow Harry has the main point nailed. In peacetime you are going to need to VID your target before anyone is going to give you engagement authority - be that a Typhoon driver or a helicopter with a sniper. Even then, if inside the M25 there is a thought that you may as well just let it hit rather than schwack it and let the debris fall randomly over the ~8M populace. Depending on the professionalism of the suicide pilot then it may well miss any strategically critical assets anyway!
LJ