Thank you for your reply about 17-year-olds and quad bikes. I hope that you'll find the following information helpful. Although the driving licence regulations generally require a provisional licence holder on the road to be accompanied by a supervising driver, this does not apply if they are driving a vehicle in licence categories B1, B1 (limited to invalid carriages), F, G, H, or K, provided the vehicle was constructed to carry only one person. A 17-year-old driver with the B1 category on his/her provisional licence would be able to drive a single seat quadricycle on the road, provided that vehicle was suitable for road use, and it met the description of driving licence category B1 (3- or 4-wheeled vehicle with an unladen weight not exceeding 550kg).