Chris,
A, B, C, and bronze are nationally managed. Silver, Gold, and higher are managed by the FAI. In Oz and the UK soaring has traditionally been club-based rather than managed through the CAA/CASA/etc. In most European countries, as well as the US, soaring is managed through the FAA, LBA, or whatever TLA (three letter acronym) some country uses.
The club-based system has a long history of safe flying without big government oversight. This approach has allowed visiting pilots in the UK and Australia to get a local checkout and fly. (In Germany you can fly a D-reg glider with almost any foreign glider license and a medical.)
Side note, I looked at the BGA FAQ page(s) and found that you can go through them to get an EASA license now. Though I still think that a CPL holder who lives in Spain would find it simpler to do at home than risk weather delays in the UK.
Terry