4.—(1) Subject to sub-paragraph (2), the period during which a certificate is in force shall commence on the day specified in the certificate as being the date on which it comes into force and shall continue for the life of the person concerned.
(2) If in any case the Department determines that the condition specified in paragraph 3(2)(b) is not satisfied, the certificate shall cease to be in force from the date of such non-satisfaction as determined by the Department (or such later date as appears to the Department to be reasonable in the circumstances).