4. These Regulations apply in relation to every motor vehicle (other than a land tractor) manufactured on or after 1st July 1973, being a vehicle which—
(a)has four or more wheels; and
(b)is so constructed as to be capable of exceeding a speed of 25 kilometres per hour on the level under its own power,
and to every trailer which is manufactured on or after that date, being a trailer drawn by such a motor vehicle.