General Rate Act 1967

7 Where a rebate application in respect of, or of part of, a hereditament is made by a person who did not become entitled to make it until more than one month after the beginning of the rebate period to which it relates, then—

(a) if the rating authority to whom the application is made are satisfied that, for that rebate period, the applicant has made or is liable to make (and neither is nor will be entitled to recover) a payment by way of rates or rent entitling him to apply for a rebate in respect of, or of part of, some other hereditament, the amount of the applicant's reckonable rates shall be increased by that sum or 15s., whichever is the less;

(b) in any other case, the amount of the applicant's reckonable rates shall be increased by an amount bearing the same proportion to 15s. as the part of the rebate period to which the application relates falling before the date when the applicant became entitled to make it bears to the whole of that period.