3. Nothing in these Regulations applies to—
(a)an invalid vehicle, that is a vehicle the unladen weight of which does not exceed 254 kilograms and which is specially designed and constructed, and not merely adapted, for the use of a person suffering from a physical disability and solely used by that person; or
(b)a pedestrian-controlled vehicle, that is a vehicle the unladen weight of which does not exceed 450 kilograms which is neither constructed nor adapted for the carriage of a driver or passenger.