In reply to noteviljoe:
Why wait until March?!
There are very few you need to sign up for. Just turn up on the day, pay a fiver, run and have cake and tea in the Scout Hut/Village Hall afterwards - sometimes tea and cake is even free! The shorter races are generally marked/marshalled so you won't have to worry about navigation.
No membership, speed requirements or anything else required. Just choose a race distance you're happy with from FRA website and probably start with a C category race. A to C denotes steepness, A being steepest, C the least steep. S, M and L denote short, medium and long. See FRA website, the codes will help you when scanning race listings.
Have fun, fell running is a great little sub culture!
PS, you're right - running on roads is very dull!