Any person who uses on a road, or causes or permits to be so used, a goods vehicle when an alteration has been made to the vehicle or its equipment which is required by regulations under the said section 45 to be, but has not been, notified to the Secretary of State shall be guilty of an offence.
In any proceedings for an offence under subsection (3) above, it shall be a defence to prove that the alteration was not specified in the relevant plating certificate in accordance with regulations under the said section 45.
The Secretary of State may by regulations—
(a) exempt from all or any of the foregoing provisions of this section the use of goods vehicles for such purposes or in such an area as may be prescribed ; and
(b) make provision for the issue in respect of a vehicle in such circumstances as may be prescribed of a certificate of temporary exemption exempting that vehicle from the provisions of subsection (1) or (2) above for such period as may be specified in the certificate.