12. Any pressure system being carried in a vehicle if the vehicle–
(a)is engaged in an international transport operation within the meaning of the ADR;
(b)complies with the conditions contained in Annexes A and B to the ADR; and
(c)is certified pursuant to the ADR as complying with it,
or if the vehicle is engaged in a transport operation subject to a special bilateral or multilateral agreement to which Article 4 of the ADR refers and to which the United Kingdom is a Contracting Party.