Pielander, there are gliding clubs at Sutton Bank (Yorkshire GC), Pocklington (Wolds GC) as well as Rufforth (York GC, I think the one you had looked at).
Approximate locations are shown on the BGA website
http://www.gliding.co.uk/ then click on Club Directory, and then UK Club map; or just click on the names of clubs in Club Directory to link to their own sites.
UK Glider pilots do not have licences, generally (though one has been invented in an attempt to get easier recognition in other countries). There is a progression in training, which would be much abbreviated for a current PPL, through basic handling, gliding airmanship (some is different or specialised compared with power flying), coping with emergencies such as launch failure and too low in circuit, hence to solo, then escalating levels of attainment. The latter go via Bronze (soaring ability - two sustained flights + flight test and exams on weather, air law etc.), cross country endorsement - field selection etc.; Silver - a 5-hour soaring flight, a 50km cross country with limited height start,and a 1000m height gain; Gold - a 300km cross country flight, and 3000m gain of height; Diamond - a 500 km cross country, a 300km closed circuit flight which ends in a return to the start, and a 5000m height gain. After that, diplomas for 750km, 1000km, etc.
There are competitions for those who want them, usually based on speed round a closed-circuit task each (flyable) day for a week or more.
A few glider pilots do aerobatics at competition level, rather more do some mild ones for their own pleasure. Most soaring gliders are limited to simple manoeuvres - loops, spins, chandelles; no flicks or inverted flight except in specialist gliders.
Hope this helps. Chris N.