18 Summoning of witnesses
1 Subject to paragraph (2) below, the Tribunal may by summons require any person in the United Kingdom to attend as a witness at a hearing of an appeal at such time and place as may be specified in the summons and, subject to rule 27(2) and (3) below, at the hearing to answer any questions or produce any documents in his custody or under his control which relate to any matter in question in the appeal.
2 No person shall be required to attend in obedience to a summons under paragraph (1) above unless he has been given at least 7 days' notice of the hearing or, if less than 7 days, he has informed the Tribunal that he accepts such notice as he has been given.
3 The Tribunal may, upon the application of a person summoned under this rule, set the summons aside.
4 A person who has attended a hearing as a witness in obedience to a summons shall be entitled to such sum as the Tribunal considers reasonable in respect of his attendance at, and his travelling to and from, the hearing; and where the summons was issued at the request of a party such sum shall be paid or tendered to him by that party.
5 In relation to proceedings before the Tribunal in Scotland, in this rule “summons” means citation and the provisions of this rule are to be construed accordingly.