[JimW]

According to a website which seems pretty clued-up, this is not legal unless the vehicle being towed weighs less than 750kg. And as your car has to be road legal this seems pretty unlikely.

http://www.ntta.co.uk/ says in the FAQ

Q I have a motor home and want to tow a Fiat Seicento behind it using an A-frame. This car has a kerb weight under 750 kg so am I legal with this outfit?

A Sorry no is the answer. The law regards this as an unbraked trailer and you are allowed to tow up to 750 kg Gross Trailer Weight, not a car’s kerb weight. The figure you have to use is the car’s Gross Vehicle Weight or Maximum Permitted Weight. This is usually at least 300 - 400 kg more than the kerb weight. We have no knowledge of any car sold in the UK that has a GVW under 750 kg. The only vehicle we know that is completely legal to tow with an A-frame is the French Aixam small "car". This is a full four seater and details can be obtained from Aixam UK on 01926 886100. An A-frame or dolly can only be used to recover a broken down vehicle to a place of safety. Transporting a car is, therefore, illegal. A-frames may be offered with a braking system that applies the car's brakes. These do not conform to the law as the car then becomes a "braked trailer" and has to conform to European Directives contained within the Construction and Use Regulations. It does not conform to the European Directive 71/320/EEC and amendments regarding braking requirements in any way. The use of this A-frame for transportation is illegal. It is still OK for use to recover a vehicle to a place of safety.