A vehicle that is permanently imported for use in Great Britain must be registered and taxed as soon as possible after it arrives in the country. The vehicle should not be used or kept on public roads until the registration and vehicle tax formalities have been completed.
Requirements will vary depending on the age of the vehicle, whether it is being imported from inside or outside the EU, etc. For more details visit https://www.gov.uk/importing-vehicles-into-the-uk
To register your vehicle visit your nearest Driver and Vehicle Licensing Agency (DVLA) on https://www.gov.uk/contact-the-dvla