Before reporting an untaxed vehicle you should check the details online using the DVLA vehicle checker.
If the vehicle is not taxed you should report it to the DVLA.
If the vehicle does not have MOT you should report it to the Police on 101 (non emergency number) - as the Police can issue the owner with a fine. You can find more information on gov.uk.
Foreign plated vehicles cannot be dealt with by the City of Lincoln Council they should be reported to the DVLA or the Police.