80. Local authorities may combine to prepare, etc., plans---(1) Two or
 more territorial authorities may agree to jointly prepare, implement,
 and administer a combined district plan for the whole or any part of
 their combined districts.

   (2) Two or more regional councils may agree to jointly prepare,
 implement, and administer a combined regional plan for the whole or any
 part of their combined regions.

   (3) One or more regional councils or territorial authorities may agree
 to jointly prepare, implement, and administer a combined regional and
 district plan for the whole or any part of their respective regions or
 districts.

   (4) A local authority that is both a regional council and a
 territorial authority may prepare, implement, and administer a combined
 regional and district plan for the whole or any part of its region or
 district.

   (5) The relevant local authorities shall consider the preparation of a
 combined regional or district plan under this section whenever
 significant cross-boundary issues relating to the use, development, or
 protection of natural and physical resources arise or are likely to
 arise.

   (6) Such a combined plan may be prepared after consideration under
 subsection (5) or in any other case where the local authorities
 concerned consider it appropriate to do so.

   (7) Section 114S (which relates to joint committees) of the Local
 Government Act 1974 applies to the appointment and conduct of any joint
 committee set up for the purposes of this section.

   (8) Where a combined plan is prepared under this section---
   (a) It shall be prepared in accordance with the First Schedule; and
   (b) When approved by a local authority (whether or not approved by any
         of the other local authorities), it shall be deemed to be a plan
         separately prepared and approved by that authority for its
         region or district for the purposes of this Act.