I do a bit of towing with my Defender, and when the other half was moving house I went to hire a box trailer
After spending hours reading up on it I concluded that you could tow up to the Gross weight of the vehicle, so in my case 2.5 tonnes... wrong!
It's all very complicated, but the local hire place said the same thing as above. 750kg un-braked on a normal licence. Anything over that or with a braked trailer you need to sit an additional test
I wonder how many people are towing caravans illegally thinking they are ok?