Actually - I have just checked in
The Gliding Book and Alex Watson wrote a chapter on ATC gliding - he says - Cadets are not permitted to fly solo in under 20 launches unless they have previous power - flying experience.
So PJ88 was absolutely correct
He also says that in 1963 the Air Cadet gliding movement was responsible for training 2,043 Cadets to A+B badge and for that year the total number of launches was 136,345.