Phill, as you will know that is a French car and I believe the German authorities also allow this no matter the age of the (Morgan) vehicle as the trailed item also has to have an MOT.
I don't understand the logic either.
Here there is an age limit, ironically after a certain age (I don't know the cut off) Morgan's were no longer allowed to fit a tow bar.
A great shame for people that enjoy this kind of touring whilst having a great car for unhindered exploring, I know Tim has an earlier car hence my comment.
In Germany a tow bar has to be TÜV approved. Than the weight of the Morgan and other facts (trailer with/ without brakes ets.) decide on the weight that can be drawn.