Legal-er, but still not legal.
Car brakes will not, and can not meet the efficiency ratings required for trailers, which are required to be over 50% ( i think its 50%? I dont have the specs to hand here) efficient on all wheels. Car front brakes are more efficient and the rears much less so. I also believe the brakes on anything under 3.5 tons need to be mechanical and not electrical or pneumatic, and they need to auto-reverse.
There is no grey area anywhere. Unless for recovery of a broken down car to a nearby place of safety, A-frames are straight-up illegal. No ifs, no buts.
The only way an A-frame will be legal for moving a car is if the towed car has a GROSS weight of under 750kgs, which narrows you down to maybe a Caterham or other 7-type and perhaps stuff like an original Fiat 500. Even a classic mini comes in at well over 750kgs gross.
Obviously, a-frame manufacturers -especially those aimed at motorhome users- say otherwise....its in their interests to do so an the wording of the relevant laws is sufficiently convoluted that you could interpret it any way you wished if you put your mind to it, and even those who SHOULD know for certain - the police and often some VOSA employees dont know for certain either.
This is why many police will do nothing when they see one - they dont know the specifics of the laws so as long as your outfit looks decent - ie not towing a transit van with a ford escort, many will let it pass. It takes the pedantry of a well informed VOSA officer to bring out the specifics of the law and ruin your day.
Does that stop people - including me - using them? nope. A properly rigged up A-frame is an absolute pleasure to tow and inherently much more stable than a trailer. A trailer raises the center of gravity up by at least 30-40cm, and the axles spacing and overhangs of the trailer allow for it to be potentially very unbalanced, which leads to instability and snaking. The self-centering of a cars steering when its being towed eliminate this completely - no snaking, no wobbling, no weaving at any speed, uphill or down.
I have both, a good quality twin axle car transporter and an ex RAC a-frame made by Intertrade which has the capacity to work the towed cars brakes via a bowden cable and a thing which clamps to the drivers seat and brake pedal. I never use the brakes though as its pretty useless unless the cars engine is running for servo assistance.
Legalities aside - I would always choose the a-frame for shifting a car unless it will not roll for whatever reason, or is an automatic. The main down-side of a-frames is they can not be reversed at all. You can just about manage a dead-straight reverse but forget trying to turn a corner backwards - literally impossible.
