Exams
We had to pass the college exams which were based on the board of trade sylabus but to a higher standard and more comprehensive which gave us a CPL but was above ATPL standard. Iirc courses after 1972 had a frozen ATPL upon graduation.
In reality the UK knowledge requirement was higher than the FAA exams I took years later.
I visited a training establishment a few years ago and was shocked to find that one could get a cpl with a total of 160 hours without any twin solo nor spinning and aerobatics.