You can register with the BMFA as a CAA Operator (and pay the £9 fee) when you join or renew your BMFA membership. The CAA will email your Operator ID to you early in February, you are exempt from displaying the operator ID until it arrives.
If you have an existing BMFA Achievement or take the new BMFA RCC, then you have a CAA recognised competency. Job done.
It’s as simple as that!