As I understand it, gliding activity in the UK is regulated by the BGA, through a system of BGA accredited clubs and instructors. You may fly solo when your instructor thinks you are ready, and the same applies to your first cross-country flight, for which you are expected to undergo quite rigorous extra training. Before cross-country, you are expected to stay in gliding range of the airfield, but it's quite common for non X-country competent pilots to get it wrong and "land out" (did it myself a few times...)
Gliding is enormous fun, definitely increases your flying skills, and is as safe as most forms of flying (probably much safer than some). Very few accidents, most of them being mid-air collisions as a result of concentrations of gliders around gliding sites and in thermals.
I had 130 hours gliding experience over 7 years, and hold a Silver C, allowing a discount off PPL A training hours but although I was solo in a Warrior after about 9 hours, it still took me 47 hours to get the PPL A owing to considerable difficulty dealing with radio and ATC.... most of the gliders I flew didn't even have radios....