Road racing in the UK is, on the whole, organised by British Cycling and they have a good introductory page on their website;

http://www.britishcycling.org.uk/web...road_about.asp

You'll need a license and, as I'm assuming you've never raced before, then you'll start as a 4th category rider. I'd recommend you start with one of the Go Race races that BC organise for 4th cats as that'll give you a feel for it.

If you're not a member of a club then I'd recommend you join one as you'll get advise, encouragement and some people to share the experience with.

A word of warning - the barrier to entry in UK road racing is high. You have to be very fit to finish a race due to the small number of people racing so I'm afraid it'll be a bit soul destroying to begin with. But if you go in with a positive mindset and try and treat each race as a learning experience then you'll progress quickly.