13.—(1) Unless the parties agree to arbitration any difference arising between the Council and the Agency shall be settled by the Secretary of State for Environment, Food and Rural Affairs on a reference to him by either party after notice in writing to the other.
(2) Subject to sub-paragraph (1), any difference arising between the Council and the Agency under this Schedule (other than a difference as to its meaning or construction) shall be referred to and settled by a single arbitrator appointed by agreement between the parties on reference to him by either party, after notice in writing to the other, or, in default of agreement, by the President of the Institution of Civil Engineers.