I just realised that I hadn’t answered this on the Forum for the benefit of others because we had an email exchange.
Members can be deleted from Crossmember ONLY when they are in the LAPSED state. So if your member is either still a MEMBER or they are OVERDUE, you must first ‘Terminate’ their membership. This will place the member directly into the LAPSED state.
Once Lapsed, a ‘Delete’ button appears on their membership record and you can delete the member in their entirety. Any vehicles that they own will remain in Crossmember but will be assigned to the ‘unknown’ owner.