I worked in that area for over a year (a long time ago) and crossed that bridge many times. I highly doubt that the video of the guy getting up is legit.. It's odd that the video exists - I agree.. However, if this guy had gotten up there would have been many people who would have seen it imo.

There aren't really any prisons in that area and I would not have thought that any kind of prison rehab group would operate near London Bridge as it is a prime property site for business.