To compete in the road standard class, which is what I did 5 seasons of all you need to do to your car is:
Fit a timing strut to the front of the car to the dimensions and height specified by the blue book which you will get when you apply for your licence.
Put some yellow tape around the negative lead of your battery.
Put a sticker next to the ignition key indicating which way is OFF.
As a competitor you will need some fire proof overalls and an approved helmet. The first time you use the helmet you will need to pay £2 to the scrutineers for a MSA sticker to show the helmet is eligible.
Then off you go!
The beauty of SB is that the mods you can make are very limited. With Nottingham Sports Car Club the following applies to SB:
Everything standard and as it left the factory except:
Dampers may be replaced by performance items.
Tyres may be changed, but must come from list 1A of the blue book.
Both front seats may be replaced by fully trimmed competition items.
A harness may be fitted.
A rollcage may be fitted.
Simples.
The next class up is 1B (Road modified) which opens up modification of the car, however, all interior trim must remain as fitted to the car originally and all ancillaries must still operate i.e. rear wiper, electric windows etc. Tyres remain as list 1A which is also a limiting factor. In 1B, you will find some very highly modified Peugeot 205's amongst others and diffs, ITB, and coilovers are the minimum requirements really.
Your final class option is Modified Production Car which as Cr33do has mentioned, is where they would be. This class is for race cars, i.e. stripped interiors, plexi windows, fibreglass panels, 1B tyres etc etc.
As I found while competing, different clubs operate different class structures. Some don't have SB (Road Standard) so you get lumped in with the modified boys! So some events will be competitive and others not so. This said, you are racing against the clock for championship points, so an outright win isnt necessary, as long as your time for the event scores you enough points.
Scoring points at an event.
Each event has a target time allocated to it. Usually the class record, but if it is a new event to the club, a target time will be calculated.
My class record for MIRA is 57.20, which is the current target time there. If you match this time, you would score 20 points. For every 10th of a second slower, you deduct .10 of a point. So, if you finished with a time of 59.70 secs you would score 17.5 points for the event. if you beat the class record or target time, you score more points in the same way.
If you can consistently beat the target time, you are well on your way to a championship win!
Hope this helps.
Andrew