For the purposes of this Act—
(a) a mechanically propelled vehicle being an implement for cutting grass which is controlled by a pedestrian and is not capable of being used or adapted for any Other purpose, and
(b) any other mechanically propelled vehicle controlled by a pedestrian which may be specified by regulations made by the Secretary of State for the purposes of this section and section 103 of the Road Traffic Regulation Act 1967,
shall be treated as not being a motor vehicle.
In subsection (1) above " controlled by a pedestrian " means that the vehicle either—
(a) is constructed or adapted for use only under such control or,
(b) is constructed or adapted for use either under such control or under the control of a person carried on it but is not for the time being in use under, or proceeding under, the control of a person carried on it.