143.—(1) Article 141 (application of Order to Crown employment) does not apply to employment in respect of which there is in force a certificate issued by or on behalf of the Secretary of State certifying that employment of a description specified in the certificate, or the employment of a particular person so specified, is (or, at a time specified in the certificate, was) required to be excepted from that Article for the purpose of safeguarding national security or protecting public safety or public order.
(2) A document purporting to be such a certificate shall, unless the contrary is proved, be deemed to be such a certificate.