Finally ventured out around Liverpool St and Shoreditch few days ago. It's a bit hit and miss but we found an excellent wall in the corporate wankfest that is the area around liverpool street station that's sheltered from security and the elements to a degree.  Will post a photo of that next time round.  This is my mate James having a gentle clamber somewhere near Old St tube, London.

(Please keep in mind that this image is not a genuine photo but is in fact a photoshop manipulation to give the impression that someone is climbing up a building.)