Interesting reading.
I towed a 4 berth caravan from Birmingham to near Villedieu- Les- Poeles, in Normandy with my 1986 740GLE in 2003 and didn't even realise I shouldn't of as I passed my test in 1999!!
Thankfully it went very well.
I think it's a bit of a ridiculous rule as presume even if I wanted to use a builders trailer can't as need B+E?
James