To be slightly pedantic, you wouldn't be flying a glider on your PPL.
Learning to fly a glider would be helped a lot by your PPL training but the (fairly minimal) paperwork requirement to fly cross country would be issued by the BGA.
Having gone solo you could continue to fly club-owned gliders within gliding range of the airfield (which can be quite a long way!) solely at the discretion of the duty instructor with absolutely no paperwork whatsoever. But it wouldn't be a lot of fun!
The insurance companies as usual probably have more influence over who flies what than the BGA.