The rent payable for a holding may be increased during the term of the holding--
(a) if the holding's provisions specify a methodology for determining increases--in accordance with that methodology, or
(b) if the holding's provisions provide that the rent is fixed and cannot be changed during the term--in accordance with a redetermination made by the Secretary under this Division, but only where the redetermination is required because--(i) the area of the holding has changed, or(ii) of a provision of Schedule 1, 2, 3 or 4, or
(c) if the holding's provisions make no provision about whether or how rent may be increased during the term or provide for the Secretary to make redeterminations of rent under this Act--in accordance with a redetermination made by the Secretary under this Division, or
(d) if a provision of this Act or the regulations requires or permits the Secretary to redetermine rent following a change to the area, purposes or conditions of the holding (for example, under section 4.3 and Divisions 7.2 and 7.3).