18.—(1) Following receipt of the papers from the parties, the Commissioners may request either party to produce further evidence or information on any topic relevant to the conduct or determination of the case and may stay the progress of the case until a response to their request has been received.
(2) Subject to rules 14(2) and 15, any further evidence or information produced under paragraph (1) shall be served, by the party responding, on the Commissioners and on the other party.
(3) A party may not supplement or add to case papers, response papers or further evidence and information produced and served under this rule without the leave of the Commissioners, or, after the allocation of a case to a Panel, the Chairman of the Panel.