13(1)This paragraph applies to determine the amount of rent payable under a lease where that amount—
(a)varies in accordance with provision in the lease, or
(b)is contingent, uncertain or unascertained.
(2)The provisions of this Act apply as in relation to other chargeable consideration and accordingly the provisions of sections 18 and 19 apply if the amount is contingent, uncertain or unascertained.
(3)But section 20(b) does not apply.
(4)For the purposes of this paragraph, the cases where the amount of rent payable under a lease is uncertain or unascertained include cases where there is a possibility of that amount being varied under—
(a)section 13, 14, 15 or 31 of the Agricultural Holdings (Scotland) Act 1991 (c.55), or
(b)section 9, 10 or 11 of the Agricultural Holdings (Scotland) Act 2003 (asp 11).
(5)No account is to be taken for the purposes of this paragraph of any provision for rent to be adjusted in line with the retail prices index, consumer prices index or any other similar index.