Use of Invalid Carriages on the Highways Regulations 1988
According to the above regulations the use of mobility scooters and wheelchairs fall into one of the following three groups:
Manual wheelchairs, i.e. self-propelled or attendant propelled, not electrically propelled. These are not required to be registered with DVLA.
Powered wheelchairs and scooters intended for footway use only with a maximum speed of 4mph and an unladen weight not exceeding 113.4kgs. These are not required to be registered with DVLA.
Mechanically propelled invalid carriages that are constructed or adapted to be capable of exceeding a speed of 4mph but incapable of exceeding a speed of 8mph on the level under its own power (generally powered wheelchairs and other outdoor vehicles including scooters intended for use on roads/highways). They must be fitted with a device capable of limiting the maximum speed to 4mph for use when travelling on footways. The unladen weight must not exceed 150kgs. These are required to be registered with DVLA
If you are alert to such things you may see legal infringements all around. At the time I knew of 2 or 3 mobility scooter users and would often see the big class 3 scooters careering along the footpath or equally worrying, little old ladies in little class 2 scooters ambling down the middle of the busy, main road.