Andrew,
I happened to have my old logbook on my desk as I read your post.
I learned to fly in a Piper Colt at White Waltham in 1966 on an RAF Flying Scholarship. My first flight was on the 3rd September, and I went solo four days later, after eight flights, including one in a Chipmunk for the mandatory spinning exercise. Total time 7:35. Exercises: Famil, 3 to 13. The last three flights before solo were circuits (12 and 13).
The continuity probably helped a lot and we operated non-radio, which also reduced the work-load, but my time wasn't particularly remarkable. Other members of my course all went solo with about the same number of hours.