(1)A certificate may be reviewed by the Secretary of State—
(a)either within the prescribed period or in prescribed cases or circumstances; and
(b)either on an application made for the purpose or on his own initiative.
(2)On a review under this section, the Secretary of State may—
(a)confirm the certificate;
(b)issue a fresh certificate containing such variations as he considers appropriate; or
(c)revoke the certificate.
(3)But the Secretary of State may not vary a certificate so as to increase the total amount specified unless it appears to him that the variation is required as a result of his having been supplied with incorrect or insufficient information by the applicant for the certificate.