31.—(1) Subject to regulation 29(2), for the purposes of identification, a certificate of Crown exemption shall be displayed on every vehicle belonging to the Crown which is used or kept on a public road.
(2) A certificate of Crown exemption is a certificate—
(a)marked with the registration mark of the vehicle to which it relates;
(b)stating that the vehicle is exempt from vehicle excise duty as a Crown vehicle;
(c)signed by a duly authorised officer of the Government Department by which the vehicle is kept.
(3) Regulation 7 (exhibition of vehicle and nil licences) of these Regulations shall apply as if references to a vehicle licence included a reference to a certificate of Crown exemption.