I've seen them close to Covent Garden before. Bob wasn't on a harness or anything, just sat in the middle of the pavement completely oblivious to the noise, commotion and general business around them - it wasn't a quiet day as it was lunch time and was busy! I couldn't believe he would sit there totally unconcerned.
Looks like they may have a book out as well at some point as there is one on pre-order at Amazon.