Where is this?

I'm in London for the Internet Librarian International conference, starting today.
On my way to the conference I saw this small mosaic. It is part of a much larger art work. The tile-sized mosaics (all of a swallow but done by different people) are placed in different places around the world, linking into one world-wide piece of art!
This one is London - Do you know where it is?  
If you think you do (or if you've given up) check the map!