The UK starting point: EAPC rules
In Great Britain, an electric bike can be treated as an electrically assisted pedal cycle, or EAPC, when it meets the relevant requirements. GOV.UK states that an EAPC must have pedals capable of propelling it, a motor with no more than 250 watts continuous rated power, and electrical assistance that cannot propel the bike above 15.5 mph. Riders must be 14 or over.
A compliant EAPC does not need a driving licence, registration, vehicle tax or compulsory motor insurance. It can be ridden where pedal cycles are allowed, but not on pavements.
What about faster or more powerful e-bikes?
If an electric bike falls outside the EAPC rules, it can be treated as a motor vehicle. That changes the legal requirements significantly. Do not assume that a higher-powered or faster model is simply a more capable version of a normal e-bike.
Twist-and-go and approval
Some electric bikes can provide motor assistance without pedalling. GOV.UK explains that an electric bike with this capability may require vehicle approval, depending on how it is configured.
Why this matters when buying
Legal compliance should be checked before looking at performance figures. The safest buying journey is to identify the type of riding you need, then confirm that the model is intended and approved for the way you plan to use it.