If you google for munch groups in London you will find that there are lots of kinky people around. A munch is a meeting of people who enjoy BDSM for a drink or meal, somewhere mainstream, no fetish clothing required. There are also places like Torture Garden, where you can get dolled up and have some fun.
I can highly recommend the BDSM Library here, which has lots of information on more practical aspects of BDSM like safety, the principles of consent, safewords etc. Knowledge is indeed power and whichever side of the whip you want to be on, doing your homework is a real must.