Are you asking about buggies or bicycles?
Bicycles:
Electric-assist cycles & UK law
In the UK, riders must be at least 14 years of age.
Electric cycles are classed as pedal cycles provided they conform to the pedelec definition (motor power output inversely related to speed, and power cut whenever the rider stops pedalling) and have a powered-assisted maximum speed no greater than 25kph (16mph, but you can pedal faster unassisted). They must also have average power output limited to 200W (250W for an electric tricycle or tandem) and weight limited to 40kg (60kg for a tricycle or tandem).
Mobility buggies /scooters
http://www.scootamart.com/mobility-scooter-reg ulations.htm