18.—(1) Before commencing the construction of, or the carrying out of any work which involves interference with a highway, the undertaker must submit to the relevant highway authority for its approval plans, drawings and particulars (in this paragraph referred to as “plans”) relating to the works, and the works may not be carried out except in accordance with the plans submitted to, and approved by, the relevant highway authority.
(2) If within 28 days after the plans have been submitted the highway authority has not approved or disapproved them, it is deemed to have approved the plans as submitted.