Let's assume I know nothing about long O style races. What are the best long nav races in the UK?
Mountain marathons? Mountain trials? Chases?
They are all different...
so it depends what you are looking for.
Pure long orienteering would be the Tim Watkins
Classic fell navigation the Mountain Trial
Demanding MM - Lowe Alpine (but that has stopped)
MM with camp facilities Saunders / GMC
The classic - KIMM (or OMM as they call it)