You should read the supplementary Regulations 2026 CAR-nival Rally – Abingdon Motorsport CAR-nival first to determine ensure that your club is a member of an invited association or you are registered for a championship this is a round of (SR4) and which Class you are entering (SR6) is correct.
If you are NOT a member of a club that is eligible you will have to join one that is.
Craven MC
https://www.craven-motor-club.co.uk/evententries/2024-Membership-Proposal-Form-p605460768
Farnborough District MC
https://membermojo.co.uk/fdmc/
or
Sutton and Cheam MC
https://scmc.co.uk/membership/online-membership-form/