Hi Chris, just looking at the BGA map, you are unlikely to be more than 40 miles from any Gliding Club, anywhere except the remotest parts of Scotland. I used to drive 50 miles to reach a good club, which because of the fast main-roads, took me just one hour. So your gliding day needs to take into account the traveling time.
However there are clubs and there are CLUBS... Some small clubs just have a dozen members, one tea-pot, no permenant buildings, and meet only when the weather is best. You could arrive on site with just two other members, and sit in your car for a few hours waiting for conditions to improve and more people (+instructors.) to turn out.
On the other hand, some clubs have upwards of 600 members, living accomodation, club staffed canteen, internet connection, and always someone available for engineering, winching and instructing. The membership fees in both cases can be similar, as there are some 'economies to scale'. If the club has a web-cam, you can decide if conditions are Ok for what you want to do, before you set out.