Last Sunday I spent the morning walking around Camden town with Nelly from Camdenstreetarttours.com It was an amazing discovery of different works from International street artists. The demand for wall space is huge. Nelly is an inspiring personality. She negotiates wall space from landlords and invites street artists to showcase their work on them. London has become the place to be for street art and the city a public gallery with new works on display all the time. Some walls are rotated every couple of months so that new works can go up. Some stay for longer if they prove to be popular.
If you are in London I highly recommend this tour with Camden street art tours.