1. There is one theoretical knowledge exam which consists of 120 questions divided into 9 'papers'; 3 of which have 16 questions, the other 6 have 12. That was to make the 75% pass mark simple. Applicants can sit as many papers at a time as they wish.
2. Current 'all exams first time pass rate' is over 80%.
3. Many of the questions written by 'industry' (yours, perhaps Mike?) were rejected. ALL others were peer-reviewed by a group of PPL pilots, instructors and examiners - including CAA reps. No 'ex-RAF navigators' of legend were involved! We had to re-write many of them (and no, we weren't paid a penny for our assistance) before they were suitable.
4. Most failures have been from those who didn't RTFQ.
5. I don't like the limited debrief system, but it does seem to work.
At the end of the day, people have to learn the subject, not the answers. Something which some find rather taxing, it would seem....