UK Category 4 Road Racing I am seriously considering road racing, I am wondering what level of fitness I should get myself to before considering entering races. I intend to do TT races next year anyhow, but I was wondering what kind of level I would need to be so that I would generally stay in the bunch for the whole of a race.

Sort of answer I am expecting are be able to maintain 30kmh for 1 hour (on your own) or something like that, if that makes sense.
Try to figure out where the local racers do their training.  Ask your local bike store if they operate any training groups and if there are any racers in the group.  Go out with them on training runs to see if you can get a feel for where you stand in terms of fitness.  My LBS has rides once a week, and there are some racers that show up for that, but I don't see much of them after they leave.  I think this would be ideal, because even if you couldn't keep up, you could always hang back with the slower riders and have a good time.