Used one for years and most cars that were on it didn't have tax, mot or sometimes both. Never been stopped once with it. Belongs to my friend who has also been up and down the country with it with no hassle. That's not to say its legal but never had any bother, think it would depend on the mood of the copper, as seems to be a grey area.

They take a bit of gettin used to, I've also had the towing car pushed sideways by the extra wait but drive to the road conditions and they are fine, also be sensible with what you are towing, and what with.

ie using a Mondeo to tow a Fiesta was fine, but don't try it the other way around!!!