23Any question which requires, in accordance with paragraph 8 or paragraph 22 of this Schedule, to be determined by arbitration shall be determined by a single arbiter agreed upon by the parties or, failing such agreement, appointed by the Lord President of the Court of Session on the application of any of the parties to the question, and at any stage in the proceedings in any such arbitration the arbiter may, and shall if so directed by the Court of Session, state a case for the opinion of that court on any question of law arising in the arbitration.