If you are traveling to London and are anywhere around the Regent St, Soho, Piccadilly Circus, Leicester Square area then you will see a few bicycle taxis / pedicabs / rickshaws which will be happy to take you anywhere.
I know it looks romantic, even on a cold winters night but make sure you get a price BEFORE getting in the rickshaw. I have known many a person to get fleeced on these things but being over charged terribly.