These aren’t definitive, but reflect the nature of the experience offered and the level of ability needed.
Relaxed/beginner = RB
Gentle holiday tours with simple navigation or straightforward road rallies suitable for first-timers. Little special vehicle preparation needed.
Challenging/intermediate = CI
More involved UK historic road rallies and most of those in Europe. Something for navigators to get their teeth into, with a little experience beneficial. Also holiday tours with more ambitious scope and distance.
Adventurous/expert = AE
Events with the greatest commitment of time and money, plus the most exotic, costliest trips. Some racing or closed-stage rallying. International competition licence required.