q plate is if it is of indeterminate year of manufacture, eg if it has been rebuilt using a chassis of one vehicle, the body of another, and a different engine. Or if the whole thing has been modified so as to be unrecognisable, such as shortening a 110 chassis and the creating a body and drivetrain to suit. Quite a complicated issue as to why the won't issue an age related number plate, kit car builders suffer quite a lot, it all depends on how much of what part of the original vehicle remains. A kit car usually has a new chassis and body, probably an different engine. Maybe all that remains is an axle depending on the kit. Thus a Q plate is issued.