5. The Certification Officer, if in any particular case he considers it appropriate to do so,—
(a)may direct that the period for which a return is to be sent to him under Article 11(2) shall be a period other than the calendar year last preceding the date on which the return is sent;
(b)whether a direction under sub-paragraph (a) is given or not, may direct that the date before which any such return is to be sent to him shall be such date (whether before or after 1st June) as may be specified in the direction.