I am indeed a member! It really is the only way to ride in London, they have your regular weekly lessons at a few centres in London and some just a short train journey out of London, but do many other exclusive events too. XC clinics, SJ clinics (one at Bedgebury in a few weeks with John...
You could always try The Riding Club London (www.ridinglondon.com) - they do special membership for beginners and source the best riding centres in and around London. They hold lessons at Mudchute and you don't have to be on their waiting list to get in. Lots of exclusive socials and events too!