4. For the purpose of requirements 4 and 9 in the Table, in determining whether brakes apply to at least half the wheels of a vehicle, not more than one front wheel shall be treated as a wheel to which brakes apply unless the vehicle is—
(a)a locomotive or motor tractor with more than 4 wheels;
(b)a heavy motor car or motor car first used before 1st October 1938;
(c)a motor car with an unladen weight not exceeding 1020 kg;
(d)a motor car which is a passenger vehicle but is not a bus;
(e)a works truck;
(f)a heavy motor car or motor car with more than 3 wheels which is equipped in respect of all its wheels with brakes which are operated by one means of operation; or
(g)a track-laying vehicle.