5. When any person has paid the tax in respect of a motor vehicle he shall be entitled, on production of a certificate signed by the registering authority stating that-(a) the certificate of registration and the registration card granted in respect of such vehicle has been surrendered, to a refund for each complete calendar month of the period for which such tax has been paid and which is unexpired on the date on which the certificate of registration was surrendered, of an amount equal to one-twelfth of the tax payable for the year in respect of such vehicle, or (b) an application for the registration or for the renewal of the registration of such vehicle has been refused, to a refund of the tax paid.