London Gliding Club is a professionally run club which operates 7 days a week. I don't know much about the Essex club but, from their website, they only operate 3 or 4 days a week and, like most clubs, probably relies on members for winch driving and instructors etc. Also probably more friendly than LGC which can be friendly if you happen to be learning with friendly people.
In my experience, instruction can be a bit haphazard in clubs which are run entirely by the members but, if you are not in a hurry, will be cheaper and more fun.