Every day on my walk to work through the Barbican and on to Spitalfields I pass a number of graffitti-covered walls. I often wish I had the nerve to paint something so publicly, but actually it is the humour I often admire most.

There is something about the boldness of street art that makes you examine it more closely than you would an outdoor poster. Maybe that is why I am not surprised that advertising agencies see it as a useful tool. By painting a picture on a wall it becomes more permanent, more like street furniture than an advertisement. And it becomes part of the community - perhaps that is what lends it a degree of endorsement.

And if a brand can use street art to communicate a message and liven up a dull area, then it is win-win for everyone.