There is no statutory limit on the size of motors of powered wheelchairs or mobility scooters (referred to as invalid carriages in legislation). They are limited to specific maximum speeds and to maximum unladen weight limits when in use on the public highway.
The use of mobility scooters and powered wheelchairs is covered by the Use of Invalid Carriages on Highways Regulations 1988. These regulations divide powered mobility vehicles into two main categories. The Class 2 type can travel at speeds of up to 4 mph and is primarily intended for use on the pavement. The unladen weight should not exceed 113.4 kilograms. The Class 3 type can travel at speeds of up to 8 mph and can be used on both roads and pavements. Class 3 scooters must have the facility to be driven at no more than 4 mph when used on the footpath. The unladen weight should not exceed 150 kilograms. The regulations also subject Class 2 and Class 3 vehicles to requirements concerning their means of stopping. They further specify that in order to use a powered mobility vehicle a person must be “suffering from some physical defect or physical disability” and that a Class 3 vehicle must not be used by a person under 14 years.