In the case of heavy locomotives and light locomotives, two persons shall be employed in driving or attending the locomotive whilst being driven on a highway, and where any such locomotive is drawing a trailer or trailers on a highway one or more persons, in addition to the persons employed as aforesaid, shall be employed for the purpose of attending to the trailer or trailers at the rate of one such additional person for each trailer in excess of one:

Provided that this subsection shall not apply to a road roller while engaged in rolling a road.

Where a motor vehicle other than a heavy locomotive or a light locomotive is drawing a trailer or trailers on a highway, one person, in addition to the driver of the vehicle, shall be carried either on the vehicle or on a trailer for the purpose of attending to the trailer or trailers.

For the purposes of this section " trailer " does not include a vehicle used solely for carrying water for the purposes of the drawing vehicle or an agricultural vehicle not constructed to carry a load.

If a person causes or permits a motor vehicle or trailer to be driven or drawn in contravention of this section, he shall be guilty of an offence.

The Secretary of State may by regulations vary the requirements of this section in respect of any class of motor vehicles or any class of trailers, and regulations made under this subsection with respect to a class of vehicles may make different provision in different circumstances.