25Where the rating authority are for the time being affording the applicant any relief from the relevant rates under section 53 of this Act or section 2 of the [1964 c. 18.] Rating (Interim Relief) Act 1964, they shall afford the rebate only if, and to the extent that, the amount thereof exceeds the aggregate amount afforded the applicant by way of such relief as aforesaid in that rebate period.