If it is on a bar it stops being a car and becomes a trailer, to be correct you should put a light bar and registation number off the towing car. I had a friend who towed , a an A bar, an auto test mini, no front lights or doors, MOT or tax. the rear lights were plugged into the towing socket on the towing vehicle and it had the same rear number plate, he never had a problem. I am working from memory but I am sure that if you have a car being towed by a bar and nears somebody in it to stear it and use the brakes, they do not need a driving licence (this may have been stopped, it comes from very old vehicle law).