Also bear in mind that some local clubs attract sizeable fields. My own local club has a triathlon contingent which makes things busy. I don't think anyone has been turned away, but still best to let the club know you intend to turn up just so they are aware. Naturally, the club riders are given preference over those who are unaffiliated or affiliated to another. Our summer 10s are £2 (just finished, as the evenings draw in, but commence again in April/May next year).
This is, however, the time of year for hill climbs. A peculiar type of fun. Like cycling with a plastic bag taped over your head.
It's probably been mentioned elsewhere, but the CTT has lots of little rules that are easy to get caught out by. Things like club colours and sponsored shirts. Another reason to speak to people before turning up.
PS: If you are fast, turn up to an evening 10 on a mountain bike with nobblies and rip half the field a new one. That always goes down well