1If, in relation to a dwelling-house which immediately before 8th June 1968 was let on or subject to a controlled tenancy within the meaning of the [1957 c. 25.] Rent Act 1957, the relevant enactment in force at that time for the purpose of determining whether any land or premises let together with such a dwelling-house was to be treated as part of the dwelling-house was proviso (iii) to section 12(2) of the Act of 1920 (and not section 3(3) of the Act of 1939), then, in relation to that controlled tenancy, for section 26 of this Act there shall be substituted the following section:—
“26For the purposes of this Act, any land or premises let together with a dwelling-house shall, if the original rateable value of the land or premises let separately would be less than one-quarter of the original rateable value of the dwelling-house, be treated as part of the dwelling-house ; and for the purpose of this subsection "the original rateable value" means the value which, before 8th June 1968, was the rateable value for the purposes of the Increase of Rent and Mortgage Interest (Restrictions) Act 1920”.