15.—(1) On the application of a party or on its own initiative, the Tribunal may—
(a)by summons (or, in Scotland, citation) require any person to attend as a witness at a hearing at the time and place specified in the summons or citation; or
(b)order any person to answer any questions or produce any documents in that person's possession or control which relate to any issue in the proceedings.
(2) A summons or citation under paragraph (1)(a) must—
(a)give the person required to attend 14 days' notice of the hearing or such shorter period as the Tribunal may direct; and
(b)where the person is not a party, make provision for the person's necessary expenses of attendance to be paid, and state who is to pay them.
(3) No person may be compelled to give any evidence or produce any document that the person could not be compelled to give or produce on a trial of an action in a court of law in the part of the United Kingdom where the proceedings are to be determined.
(4) A summons, citation or order under this rule must—
(a)state that the person on whom the requirement is imposed may apply to the Tribunal to vary or set aside the summons, citation or order, if they have not had an opportunity to object to it; and
(b)state the consequences of failure to comply with the summons, citation or order.