Where under this Order (including any provision incorporated in or applied by this Order) any difference (other than a difference to which the provisions of the 1965 Act apply) is to be determined by or referred to arbitration, then the difference must be referred to and settled by a single arbitrator to be agreed between the parties or, failing agreement, to be appointed, on the application of either party (after notice in writing to the other), by the President of the Institution of Civil Engineers.