There's a few easy things you can do.
1. Join a club.
There's hundred of clubs in the UK and each will have many riders of different levels as well as riders who don't necessarily want to ride hard all the time. Maybe right now a Sunday morning club run with the old timers who can impart some useful advice and cycling etiquette will help you get enough seat time and used to riding in a bunch. Mix it up with midweek time trials (yes you can do these on a road bike) or some runs with the local "chain gang"...
2. Enter races.
Time trials are the easiest races to get into. Normally 10, 25, 50 or 100 miles. There's a few 12 and 24 hour events too. The 10's and 25's will be best for you right now and most districts (they follow county boundaries usually) offer a few time trials each weekend during the summer. Some clubs offer midweek time trials too.
Road Races require a license from British Cycling. You enter the races and if you finish at or near the front then you gain points towards an upgrade. This ranking system means that you won't start racing against the likes of Team Sky should they decide to ride a few events at home...
3. Find a coach.
Unlike America, coaches don't cost an arm and a leg. I remember back in the 90's paying $5 per week and that included two turbo training session sessions on a very expensive Kingcycle rig and tea and biscuits after the sessions and after races too if he went out to watch or to give one of us a ride!
abcc.co.ukabccFindACoach.aspxOpen ↗
In addition there's a number of good coaches available on line too but this usually seems to work out better if you have a power meter or cycling computer than can record the data of your rides so you can send them to the coach. Ric Stern and Alex Simmons offer sound advice and can be found at RST Sports for example - those guys hang out on these forums too and provide lots of good advice, hence the shameless plug. Alex is a sound bloke and an inspiration.
4. Don't forget the obvious. Fun!
For most of us its about having fun. If it's not going to be paying the bills then it's all about fun. While you should spend some time figuring what you might want to do when you start out try it all. Whilst it might not seem obvious when you're hanging on for dear life on the back of the bunch during your first road race, lungs on fire, legs hurting even more than your lungs... at the end of the race you should be able to gain some satisfaction from it and a desire to get better.