There are / were a couple of other SE1 Bankys, neither of which seem to have been spotted by artofthestate. I took photos of both. One, [now sadly disappeared] was a little lamb on a rusting iron door in one of the London Bridge road tunnels. The other a little girl, again on a door. It has been there for several years, but following the publicity about the prices his stuff is fetching, it was recently covered with a piece of plywood - at least it hasn't been painted over....
There is a really nice Banksy exhibit (free) at the Andipa Gallery, Walton Street, SW3 with signed prints available at another site across the road. Its quite difficult to find - but I took the 360 bus from E & C and got off as it hit the Brompton Road. Whilst the exhibit is free to visit you would need to be a significant lottery winner to buy any of them. I felt unable to risk my pension lump sum. Exhibit was well attended this Tues pm and a lot of fun.
I would say that wasn't a Bansky. It looks like only one stencil layer. There have been a god few Banksys around SE1, that i remember over the last 4 years or so. There was a 'Girl with Balloon' on Clink St a few years ago. I managed to gert an official print of it in 2004.
There were at one point 3 or 4 versions of Girl with Balloon along the river between Blackfriars and London Bridge - all gone now. I think the Clink Street one was the last to go. There is a thread somewhere about Wagamama 's being annoyed when the council painted over it.