Have camera - will dialogue...
I was wandering back to my hotel after a late meeting and saw this guy playing sax near Embankment Tube station. He was not, as it happened, too pleased that I was photographing him. It turned out that Rodney Rock (yes, real name) had just been moved on by the police for the crime of playing beautiful, really beautiful, music on the South Bank and having a camera pointed at him was the final straw.
But photography is a conversation starter even if at first it doesn't go the way you hope. I hung out with Rodney for a while and it turned out he was a really fantastic guy. We spoke about how our civil liberties are slowly being infringed - he gets moved on for playing music and I have to carry a written script of my rights as a street photographer for when the police decide I am a terrorist.
So when you see (or better, hear) Rodney playing by the river, say 'hello' and give him some of your change. London is a better place for guys like this.