Below is a video featuring a few of the performers I've happened across during my time in London.
As I said, these are just a sample. Jubilee Gardens (where the London Eye is located), is like a carnival. Along with the dancer at the end of the video, there were people performing as statues and only move when they receive money. There are are also plenty of people in costume. I saw Captain Jack Sparrow, Darth Vader, a man dressed as an iguana, a woman pretending (very convincingly) to be a cat and others.
Below are just a few photos.