Any person interested in a listed building with respect to which listed building consent has been granted subject to conditions may apply to the local planning authority for the variation or discharge of the conditions.
The application shall indicate what variation or discharge of conditions is applied for.
Sections 10 to 15 apply to such an application as they apply to an application for listed building consent.
On such an application the local planning authority or, as the case may be, the Secretary of State may vary or discharge the conditions attached to the consent, and may add new conditions consequential upon the variation or discharge, as they or he thinks fit.
But a variation or discharge of conditions under this section must not—
vary a condition subject to which a consent was granted by extending the time within which the works must be started;
discharge such a condition.