Are any caravans over 750kg, as there can't be many cars under that. Unless it's a wierd ruling to do with the licence mentioned above.
Not withstanding the special case with the coach, the case with typical motor homes towing a car is that the car is considered to be an unbraked trailer which is where the 750kg limit comes from. If you can make the brakes work (There are kits that can actuate the handbrake) or if you put the car on an actual trailer you can tow more