581. Modification of payments in lieu of restoration under ironstone leases.

Where any ironstone comprised in a mining lease made before 1 August 19511 is worked by opencast operations in accordance with planning permission2, then if:


    (1)     the lease contains provisions requiring or enabling the lessee to pay a specified sum in lieu of compliance with any obligation relating to the restoration of the land or by way of liquidated damages for breach of such an obligation, or to return the land after restoration or upon payment of a specified sum in lieu of restoration; and


    (2)     the planning permission is subject to conditions regulating the manner in which the