Prior to the UK and Ireland joining the EU they had a common travel agreement which allowed for Citizens to travel freely between UK and Ireland, up until airlines insisted on passports you didn't need one to go between Ireland and UK, still don't on ferries, just ID. This did not cover trade but all other aspects, work, leisure etc. In May or June last year this was reaffirmed by the respectful governments that this would remain the case. So racecars should be ok especially booked on a return booking but we will probably need to check to be sure.
