Hello Henwood
London Gliding Club (Dunstable) and Booker are both excellent operations but others are available in your region. There are gliding clubs such as LGC, Booker and Lasham which are 7 day week operations, usually with paid staff. Their costs tend to be at the higher end of the range but they can also offer "turn up, fly, and leave" type services. They are businesses more than clubs.
The alternatives are weekend-only clubs most of which are run with volunteer crews. These tend to be much cheaper but greater time inputs from all members are expected. The ambience tends to be friendlier but you are pretty much expected to be there for the day as everyone has to muck in to make it work.
Such an operation is Oxford Gliding Club at Weston on the Green ( winch launching only). It's another 25 minutes up the M40 from Booker.
You seem to be talking about weekends only, so that kind of scene might suit, especially if finances are limited. Your choice, make some enquiries on websites etc re costs.