Hey Cats
I think the BGA recognized ATC Instructor ratings from B Category upwards (in the old days it used to be 'B' Cat as Assistant Rated Instructor and 'A' Cat as Full Rated Instructor) and they did not recognize the G2/G1 or 'C' Category.
Whether that still holds I'm not sure but that said, there is a potential pool of ready made instructors there for the BGA !!
As someone who has lived in both worlds there is no need to have a Silver C to teach someone to glide, and experienced instructor in either camp can achieve that. I would say that ATC instructors from 'B' Category upwards have a better theoretical knowledge than many BGA Instructors but the BGA Instructors have a better knowledge of teaching more advanced exercises (including the cross country elements) - so 6 of 1 and half a dozen of the other !
Arc