The pictures seem to vary quite a bit in number, the 1941 version of the pamphlet Keith mentioned says that an instructor should only take 4 to 6 students at a push at any time which does seem to match the number of machines in the pictures so maybe the others were on theoretical parts of the course or just watched and waited their turn?
Another one, with a WD/CO, M20, 16H, M20 and...??? Small headlamp, bulb horn, reminds me of the experimental lightweights. What is this...? A BSA WB30 perhaps?