26.—(1) Subject to rule 25(4) and to paragraph (2) of this rule, the Commission may, on the application of a party or on its own initiative, issue a summons requiring any person in the United Kingdom—
(a)to attend as a witness at any hearing before the Commission; and
(b)at the hearing, to answer any questions or produce any document in his custody or under his control which relate to any matter in issue in the proceedings.
(2) No person shall be required to attend a hearing in compliance with a summons issued under paragraph (1) unless—
(a)the summons is served on him; and
(b)the necessary expenses of his attendance are paid or tendered to him.
(3) Where a summons is issued at the request of a party, that party must pay or tender the expenses of the witness.