" Trailers having a maximum laden weight not exceeding 750kg are not required to have brakes fitted. However, if the trailer (regardless of mass) is fitted with a braking system, then all brakes in that system must operate correctly and efficiently. This means that the braking systems of small ‘microcars’ (under 750kg in weight) must still operate, even when the vehicle is being towed. Unless the vehicle is broken down, when C&U makes special provision."
So, basically, any car being towed fitted with brakes, as most have, is being towed illegally as the brakes are not operated. The situation on the Continent, regardless of Brexit, is grey. But many get stopped and fined. Most use a small trailer these days..
So, basically, it is the "hysterical female horse owner situation" where most law enforcement officers know wiser than to stop these people as one ends up with a lot of problems and no real solutions.
I, for one, just took the time and money to have all licences and a few more to drive & tow anything...