81.—(1) A development plan shall include an objective to preserve the character of a place, area, group of structures or townscape, taking account of building lines and heights, that—

(a) is of special architectural, historical, archaeological, artistic, cultural, scientific, social or technical interest or value, or

(b) contributes to the appreciation of protected structures,

if the planning authority is of the opinion that its inclusion is necessary for the preservation of the character of the place, area, group of structures or townscape concerned and any such place, area, group of structures or townscape shall be known as and is in this Act referred to as an “architectural conservation area”.

(2) Where a development plan includes an objective referred to in subsection (1), any development plan that replaces the first-mentioned development plan shall, subject to any variation thereof under section 13, also include that objective.