12.—(1) This article applies to a lease granted prior to the commencement date (to which the provisions of Schedule 17A to the 2003 Act apply) where there is a variation of the lease after the commencement date to increase the amount of rent, which, if it had been before that date, would have been a variation to which paragraph 13(1) of that Schedule would have applied.
(2) Where this article applies—
(a)the variation of a lease referred to in paragraph (1) shall be treated as the grant of a lease; and
(b)the chargeable consideration (other than in respect of any premium) shall be the additional rent.