18.—(1) Subject to regulation 19(2) below, where the Secretary of State has received a notice from a returning officer under regulation 17(8) above, a by-election shall be held to fill that vacancy.
(2) The period within which the poll at any by-election which is required to be held under paragraph (1) above must take place is six months from the date on which the Secretary of State receives the notice referred to in that paragraph.