Registration requires completion of a V55/4 form for new vehicles or a V55/5 form for used vehicles (both available from all UK post offices) with all necessary supporting documents. For full details click here www.dvla.gov.uk/vehicles/exptimpt.htm .
Visitors to the UK may use a vehicle displaying foreign number plates for up to 6 months (within a 12 month period), provided that all taxes are paid in your country of origin.