Photography in derelict places

[Answerprancer]

I wonder if anyone can advise me on this.
I am looking for derelict/delapidated buildings (hospitals/schools/factories ...houses) where I can either
a) easily obtain permission to enter
b) gain entry without getting caught - preferably with the minimum of disturbance and not involving any damage to boarding/locks etc.

I live in SW London so ideally I am looking for places in that vicinity.

Why ? you may ask ..here's an example of why:
http://www.reflecting...9/h1AB5E014#h1ab5e014

[Answerprancer]

Your pictures are fine Doc - not sure about your taste in beer gardens though ;-)