8Where, under section twenty-four of the Finance Act, 1943, a joint and several liability is imposed on any persons, the rights of those persons respectively to a post-war refund shall be based on the amounts of tax ultimately borne by them respectively by reason of the imposition of the liability and not on the amounts of tax paid by them respectively to the Crown, and no sum shall be paid as or on account of a post-war refund in the case of any of those persons unless the Commissioners are satisfied as to the amounts so borne by all those persons and are further satisfied that any liability of any of those persons to make a payment to any other of those persons which arises by virtue of subsection (3) of the said section twenty-four has been extinguished.