10. A person is to be treated as having ceased to be a member of a political group when—
(a)he has ceased to be a member of the authority;
(b)he has notified the proper officer in writing that he no longer wishes to be treated as a member of the group;
(c)there is delivered to the proper officer a notice under regulation 8 or 9(b) signed by the person whereby a new political group is constituted or he joins another political group; or
(d)there is delivered to the proper officer a notice in writing signed by the majority of the members of the group stating that they no longer wish him to be treated as a member of it.