STANDTO, yes most of the UK is covered by aerial photos. We use a collection of CD entitled Citiviewer for Merseyside, and very good it is to. For helping us ID the house that we need to take photo's of!
What it doesn't show are things like: what side are front/rear door hinges, what's around the side not seen on the CD, are there a couple of steps on the path or a low slung washing line. Stereo shots will even allow you to work out the height of fences and garden walls. All useful stuff for a rapid entry, but you need to get down and dirty to take them.
Again a seperate "recce bird" leads to more expense: sat around doing nothing, keeping crews current etc. People around here are used to our aircraft, so it doesn't arouse that much attention when taking photo's. People would soon learn that we had a "special" one for taking photo's.