Motorized bikes possibly not motor vehicles under UK law.

“motor car” means a mechanically propelled vehicle, not being a motor cycle or an invalid carriage, which is constructed itself to carry a load or passengers and the weight of which unladen—
(a)if it is constructed solely for the carriage of passengers and their effects, is adapted to carry not more than seven passengers exclusive of the driver and is fitted with tyres of such type as may be specified in regulations made by the Secretary of State, does not exceed 3050 kilograms, .
(b)if it is constructed or adapted for use for the conveyance of goods or burden of any description, does not exceed 3050 kilograms, or 3500 kilograms if the vehicle carries a container or containers for holding for the purposes of its propulsion any fuel which is wholly gaseous at 17.5 degrees Celsius under a pressure of 1.013 bar or plant and materials for producing such fuel, .
does not exceed 2540 kilograms in a case not falling within sub-paragraph (a) or (b) above, .
“motor cycle” means a mechanically propelled vehicle, not being an invalid carriage, with less than four wheels and the weight of which unladen does not exceed 410 kilograms,

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Although this is the legal definition, ultimately it is a matter of fact and degree for a court to interpret as to whether or not a vehicle is a motor vehicle at the time of the incident.

The term mechanically propelled vehicle is not defined in the Road Traffic Acts. It is ultimately a matter of fact and degree for the court to decide. At its most basic level it is a vehicle which can be propelled by mechanical means. It can include both electrically and steam powered vehicles.

Intended or adapted for use on roadsis also not defined by statute and again ultimately a matter for the court to decide based on the evidence before it.

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Burns v Currell [1963] 2 All ER 297

B was found sitting in a go-kart. The kart had a rear-mounted engine, a tubular frame, a single seat, silencer, steering wheel and column, but had no handbrake, horn, springs, driving mirror or wings. There was evidence that B had only used the go-kart on the unadopted road once. He was convicted and he appealed on the grounds that the go-kart was not intended or adapted for use on roads and was thus not a motor vehicle to which the regulations applied.

The Appeal was allowed and the conviction was quashed. The test to be adopted was the 'reasonable man test'. There must be sufficient evidence before the justices to prove beyond reasonable doubt that such a 'reasonable man' looking at the go-kart would say that one of its uses would be a use on the road.

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DPP v Saddington Times 1.11.2000
S drove an unregistered motorised scooter called a 'Go-Ped' on a road whilst disqualified and uninsured. The vehicle had a 22.5cc engine and was definitely a mechanically propelled machine. However, to prove the two most serious offences, the machine also had to be a motor vehicle, i.e. a mechanically propelled vehicle intended or adapted for use on a road.
At the hearing the magistrates found that the 'Go-Ped' fell far below statutory standards and would not satisfy road traffic legislation relating to motor vehicles. They decided that the vehicle was not a motor vehicle. The DPP appealed by way of case stated and also asked the Court to declare that the machine was a motor vehicle.

The courts held that the Go-Ped was a motor vehicle.

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