Just to add a little to Astir’s post:
Pre EASA, there is no official “glider pilot licence” in the UK.
There is, however, an unofficial BGA-issued licence. I forget the requirements for it, but it is beyond Bronze.
The point is, however, if you progress as far as that before EASA licences are mandatory, it should be possible to convert it into an EASA GPL of one sort or another, I believe without further tests.
If you have further question after perusing the links Astir pointed out, you are likely to find more informed opinions at gliderpilot.net than here, which has few gliding people contributing.
HTH.
Chris N