18.—(1) The Secretary of State may require such further information as he may specify from any person in respect of his statement of case mentioned in rule 17.
(2) Any information required under paragraph (1) shall be provided in writing within such period as the Secretary of State may reasonably require.
(3) The Secretary of State shall, as soon as practicable after receipt of the further information required under paragraph (1), send a copy to the authority and to every other person who has submitted or subsequently submits a statement of case or notice under rule 17.