s 21 Change in circumstances
(1) Where an applicant has represented to the proper authority the existence of any circumstance or condition as a reason for the grant or renewal of a postponement certificate and a certificate has been granted or renewed wholly or partly in consequence of such representation, and where at any time while such certificate is in force any change occurs in any such circumstance or condition, the person to whom the certificate was granted shall immediately notify the change in the prescribed manner to the proper authority. (2) Any person who, being required to notify a change in accordance with this section, fails to do so commits an offence. (3) If at any time it appears to the proper authority that, by reason of any such change as is referred to in subsection (1) or for any other sufficient reason, the certificate ought to be revoked or the period for which it was granted or last renewed ought to be shortened, the proper authority may revoke the certificate or vary it by shortening the period for which it was granted or renewed.