As I understand it it, the current rules re 15 year old cars requires that you fit retractable seatbelts, high-level stop light, a smaller fuel nozzle (cos our unleaded pumps have a smaller nozzle then the "leaded" pumps), non-convex mirrors and side-impact bars in the doors.
Once you've done all this and have an engineer's sign-off for the mods you've basically got your car complied!! Then you need to get it licenced and registered. Then you can finally drive off into the sunset....straight into your garage ready to make the car really, really FAST!! :-)