An authorised examiner may test a motor vehicle on a road for the purpose of ascertaining whether the requirements imposed by law as to—
(a) brakes, silencers, steering gear and tyres;
(b) the prevention or reduction of smoke, fumes or vapour; and
(c) lighting equipment and reflectors,
are complied with as respects the vehicle, and of bringing to the notice of the driver any failure to comply with those requirements, and for the purpose of testing the vehicle the examiner may drive it; but a vehicle shall not be required to stop for a test except by a constable in uniform.
If a person obstructs an authorised examiner acting under this section, or fails to comply with a requirement of this section or Schedule 3 to this Act, he shall be guilty of an offence.
In this section and in Schedule 3 to this Act " test" includes " inspect" or " inspection ", as the case may require, and references to a vehicle include references to a trailer drawn thereby.