4Subject to the provisions of subsections (4) and (5) of section 32 of this Act, the rent payable by a tenant of the dwelling shall not exceed—
(a)in a case where a maximum rent with respect to the dwelling has been fixed under subsection (1) of the said section 32, the amount thereof;
(b)in any other case, and subject to the provisions of section 32(3) of this Act, an amount equal to the aggregate of—
(i)the rent at which the dwelling was last let before the improvement works were begun, and
(ii)a sum calculated at a rate per annum not exceeding the appropriate percentage of the fraction of the approved expense of executing the improvement works or of the approved proportion of that expense (according as the works were for the improvement of a single dwelling or of two or more dwellings) that fell to be borne by the applicant for the grant; and
(iii)any sum recoverable in respect of the dwelling by way of repairs increase or by way of 1957 Act increase (other than any such sum included in the rent referred to in head (i) above),
and no fine, premium or other like sum shall be taken in addition to the rent.
In this paragraph—
" appropriate percentage " means, in a case where the application for the grant was made before 3rd July 1962, eight per cent, and, in a case where the application was made on or after that date, twelve and one half per cent.;
" repairs increase " has the same meaning as in the [1954 c. 50.] Housing (Repairs and Rents) (Scotland) Act 1954 ; and
" 1957 Act increase " has the same meaning as in the [1957 c. 25.] Rent Act 1957.