The law affects two-wheeled bikes but also tandems and tricycles and is an “electrically assisted pedal cycle.” If ridden on any cycle path and anywhere else that bikes are normally allowed, the electric motor mustn’t assist you when you’re travelling more than 25 km/h (15.5mph); and the power doesn’t exceed 250 watts.
In the UK you must be over 14 years old to ride an electric bike but you don’t need a licence, nor do you need to register it or pay vehicle tax.
You may find off-road bikes that can go faster than 15.5 mph by flicking a switch, but for UK law these are not compliant with EAPC regulations for on-road use.
If your ebike doesn’t meet these regulations – either because the motor is more powerful than 250W, or if it assists you when you’re riding more than 15.5 mph – it will need to be registered, insured and taxed as a motor vehicle. In this case, you will also need a driving licence, and you must wear a motorcycle helmet.