Firstly you have to be a minimum age of fourteen to ride and electric bike in England & Scotland. Our electric bikes can be ridden here in the UK without the need of a license, road tax or insurance. Be very careful though because there are electric bikes for sale in the UK that aren't legal to use!
An electric bike for use in the UK and meeting the requirements above is know as an EPAC (electrically assisted pedal cycle) If the bike that you're considering purchasing DOES NOT meet the above criteria it is classed as a motorcycle or moped and as such would need to be taxed, insured and registered with DVLA. You'll also need a license and crash helmet to use one. It's also not permitted to use this type of cycle off road either unless you are using it on private property with the land owners permission.
Our advice would be not to consider purchasing a speed bike with a motor rated above 250 watts. Please note that we do not service, repair or offer software updates for any non-compliant electric bikes.
Source: Gov Website
Information correct as of November 2017