If it's audax you'll be doing next then you will need CTC as they don't except BC apparently.........Then you have your audax membership. I pay £50 a time I think for a five year membership and then £5+ per event. Then if your racing that can be £5 + per event you enter.
What difference does having CTC or BS membership, or not, have in respect to Audax?
I'd glanced at the Audax UK website and thought it was either Join Audax UK or pay a small levy at events for day membership?