cheers jay
You're really helping me to understand this area of rendering. I guess it'll speed up subsequent work a heck of a lot when its all figured out.
I've just found the presets for the render layers (I'd been manually hacking away at options) and it gives far better results now. I'll try and get some up so you can have a better look. It's shown that the front right building is far too high specularly and like you say there is a building or two with shadow problems.

Si