Ladyfly.
Sadly there are none. West Malling and Manston are long gone as ATC VGS's, however there is one now at Odiham which is the old West Malling VGS. BGA Clubs I haven't a clue and as for the RAFGSA, again zip. There is the Kestral Army gliding club at Odiham though if it's proper gliding you're after.
Try logging onto the BGA website, that should enlighten you. If it is the VGS thing you want, phone HQ Air Cadets at RAF Cranwell and ask for Gliding Liaison 1 or 2 (GL1/GL2) and they can help you with requirements and contact numbers etc.
Hope this helps and good luck.