Article 23 Summoning or citing of witnesses
Subject to paragraphs (2) and (3) below, the Tribunal may, at any time, either of its own initiative or at the request of any party, issue a summons, (or in relation to proceedings taking place in Scotland, a citation), requiring any person wherever he may be in the United Kingdom to do one or both of the following—
to attend as a witness before the Tribunal, at the time and place set out in the summons or citation; and
to answer any questions or produce any documents or other material in his possession or under his control which relate to any matter in question in the proceedings.
A request by a party for the issue of a summons or citation under this rule shall state with reasons—
upon which facts the witness is to be questioned and the reasons for the examination;
the documents required to be produced.
No person may be required to attend in compliance with a summons or citation under this rule unless—
he has been given at least seven days' notice of the hearing; and
he is paid such sum as would be recoverable by that witness in respect of his attendance in proceedings before the Supreme Court of England and Wales, the Court of Session or the Supreme Court of Northern Ireland.
The Tribunal may make the summoning or citation of a witness in accordance with paragraph (1) conditional upon the deposit with the Registrar of a sum determined by the Tribunal as sufficient to cover—
the costs of the summons or citation;
the sum referred to in paragraph (3)(b).
The Registrar shall advance the funds necessary in connection with the examination of any witness summoned by the Tribunal of its own initiative.