The police statement is incorrect.
The DVLA states that there are international agreements which provide for the temporary use of a vehicle in a foreign country for a limited time, usually six months in a 12 month period. A visitor to the UK may use a vehicle displaying foreign plates, provided that all taxes (including vehicle excise duty) are paid in their country of origin.
It is the responsibility for the driver to prove how long an EU vehicle has been in the country. This can be achieved by producing ferry tickets. Used or unregistered vehicles brought into the UK will be allowed to circulate freely for six months in any 12 month period without the need to register. Certain vehicles will be required to display a temporary 'Q' plate. Temporary visitor status is not appropriate to these vehicles.
If a vehicle is intended for use in excess of this six month period then it must be permanently imported for use in Great Britain; it 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.
http://www.direct.gov.uk/en/Motoring/BuyingAnd SellingAVehicle/ImportingAndExportingAVehicle/ index.htm