Perhaps is the answer! You don't say where you are, and the rules do differ in countries other than the UK. Assuming you are in the UK.
Quoted from
here. A-frames and dollies
If you attach an A-frame to a car in order to tow it with a larger vehicle, the car plus A-frame counts as a trailer.
If you use a dolly to tow a broken-down vehicle, the dolly counts as a trailer.
In both cases the usual safety regulations for trailers apply.And
Trailer brakes
Any trailer weighing over 750 kilograms must have a working brake system.So if the Morgan plus the A frame is less than 750kg, you don't run into the near impossibility of linking hydraulic brakes. No idea if a three wheeler tows nicely though on an A frame.
