One minute you suggest that the boats are custom made, or adapted, then you claim that they're designed for that amount of passengers.There is no requirement in the UK to register small ships under 24m, these are French laws being discussed. In the UK the register is voluntary unless you are planning to use the craft on inland water ways or commercially. TBH its worth the bother for the small fee (see Small Ships Register Part 3) as its a lot easier if you take your boat out of inshore waters.
In France anything up to 2.5M/6.1hp is exempt. That is your typical tender designed to get you to your swing mooring or ashore from an anchor. The Vessels being used to illegally traffick migrants are typically over 6-8m with 15hp motors and designed to carry at least 12-30 passengers. In the UK (as well as France) these are classed as passenger vessels. They need to be commercially coded and operated by a commercially endorsed skipper.
Now you claim to know the exact specification of these boats. Talk of making it up as you go along. It fits exactly.
But at the end of the day, your arguments are aimed at the "skipper" or the "master" of these boats, There is no skipper or master so your arguments are invalid.