Right

Ive phoned them up

basically if my vehicle is unladen (2.3 tons) i can tow a trailer of 1.2 tons.
which brings me to 3.5 tons all in which is the max limit.

how ever if i had 1.2 tons of say sand in the back of my truck. making the truck weigh in the 3.5 tons, i can still legally tow a trailer behind me as long as it weighs under 750kg. bringing my total weight to 4.25 ton.

so basically with nothing in my truck/unladen. i can tow anything i want as long as im not over 3,5 ton in total!

sort of good news really, as ive been fannying around the last year when there was no need to!