Parts 1 and 3 and sections 42 to 42B (and so much of this Part as relates to those provisions) shall apply to a tenancy from the Crown if there has ceased to be a Crown interest in the land subject to it.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Where there exists a Crown interest in any land subject to a tenancy from the Crown and the person holding that tenancy is himself the landlord under any other tenancy whose subject-matter comprises the whole or part of that land, the provisions mentioned in subsection (1) shall apply to that other tenancy, and to any derivative sub-tenancy, notwithstanding the existence of that interest.
For the purposes of this section "tenancy from the Crown" means a tenancy of land in which there is, or has during the subsistence of the tenancy been, a Crown interest superior to the tenancy, and "Crown interest" means—