Alan - the obvious answer if you really are a novice is Fun class, if you want to race more competitively for a little longer try Open (2 laps) or Sport usually 3 laps. Masters tends to be very competitive and is 3 laps with lots of elbows on the start straight and is there for those between 30 and 39. SuperMasters is the same age group but with a bonus lap.
If you ride more than once a week then look at Open or Sport. If you want a bit more of a race go for Masters.
Chum - I suggest that half way up Brass Monkeys doesn't make you an expert so Masters or Super Masters depending on how many laps you fancy. Top 10 consistently would make a sensible thought to go to Experts but really it isn't going to be worth your while. It is where the really fast guys with team bikes, jerseys and tough training plans hang out.