A) a frames are illegal for anything other than revovery to a safe place unless its a proper conversion operation the towed vehicles brakes.

B) Dollys are also illegal as above as they leave the rear axle of the towed car unbraked.

C) as stated you CAN tow a trailer as covered on here many times, it just has to fulfil the reululations.

For instance I can tow my 900kg nova on a trailer with a net capacity of one tonne (not overloaded) the MAM of the trailer is 1300kg (net capacity + actual mass, this is on a plate on the trailer.) I can tow that behind a vectra which weighs 1340kg (MAM of trailer less than unladen weight of towing vehicle) because the gross weight or MAM of the vectra is 1900kg and 1900+1300 is less than 3500.