35. Heavy motor cars or motor cars constructed or adapted for the purpose of forming part of an articulated vehicle and which are used for drawing only a trailer falling within a class of vehicle specified in paragraph 13, 14 or 15 of this Schedule or a trailer being used for or in connection with any purpose for which it is authorised to be used on roads by an order under section 42(1) of the 1972 Act, being an order authorising that trailer or any class or description of trailers comprising that trailer to be used on roads.