I agree with Ian Hingley about class O.
Dead end sections are a pain on a bike - Bishops Wood class O has the most ridiculous extra 15 yards into a rutted cul-de-sac. Dragging a rigid Matchless road bike out of that in 2015 (after breaking it's engine, literally, on Hangman's Hill; a one day trial hill if there ever was one {Chairman's Trial hill}) made me realise that class O wasn't really suitable for a classic road bike on trials tyres.
IMHO it seems that class O is almost where the main trial was 10 years ago, but without the 100 mile ride in, and the famous names.