Starting a new thread for you so that people see your question.
Have you tried Googling your area? I know EO has some local contacts in London. There is a group of teens in N London called the Otherwise Club.
If you are already in London, perhaps you could go to the Home Education Fair
on Saturday, 16 March 2013 from 11:00 to 17:00, Woodlands Montessori, 22 Gordon Road, Leyton, E15 2DD