9For the purposes of a rebate application in respect of any rebate period, the applicant's reckonable income shall, subject to paragraphs 10 and 11 of this Schedule, be his income in the relevant assessment period, that is to say, the period of six months ending, if the rebate period begins on 1st April, with the preceding 31st December, or if the rebate period begins on 1st October, with the preceding 30th June.