A local planning authority may, if it thinks fit and after giving public notice of its intention, enter into an agreement with—
(a) the owner of any building which constitutes existing development; or (b) the owner of any property who has established a use which constitutes or operations which constitute existing development;
where such building, use or operations do not conform to or contravene any provisions of an operative master plan or local plan or an approved scheme, to the effect that no action shall be taken by the local planning authority in terms of section thirty-five for such period, not exceeding twenty-five years, as may be specified in the agreement and section fifty-one shall in such circumstances apply.