Graffiti - the work of mindless vandals or creative practitioners? To some it is art, to others a sign we've lost control of our cities. Since Roman times graffiti has been a form of anti-establishment rebellion. But today it's transcending social nuisance to gain cultural and artistic credibility, unprecedented prices at auction and even presidential and prime ministerial approval. However, at street level a bitter war is being waged between graffiti writers, street artists and the authorities. While graffiti writers face trial and prison sentences for their art, some street artists' work is lauded and protected behind Perspex. This issue is at the heart of a graffiti war being fought on the streets of London between one of the founding fathers of the British graffiti scene and the most famous street artist in the world.