UNITE and BASSA have no collective bargaining rights for MF. Any CC member from MF that strikes would be totally unprotected and would be carrying out Wildcat sympathy action. BA could summarily dismiss them and indeed would be highly likely to.
You can be a member of a union in a workgroup without the union having any rights to speak for that workgroup. Indeed that is how many unions build membership to the point that recognition can be forced.