Interesting, i thought as long as the GTW didn't exceed 3500kg, i didn't exceed the MAM of the trailer & didn't exceed the towing capacity of the vehicle i was fine with my B licence ? Is this true?

What i have:

Range rover, kerb weight 2130kg, maximum towing capactiy 3500kg. So my horse box, which is un-plated with 66 rating tyres = 1200kg maximum weight? My box weighs 770kg which leaves 430kg worth of horse?

430kg of horse + 770kg trailer weight + 2130 of car = 3330kg gtw. give & take a few kg for passengers/fuel + still under 3500kg so all good, correct?

Things start to change however when i couple up my ifor williams hb505. MAM trailer weight 3500kg + 2130 of car = gtw of 5630kg = 2130kg too heaving for my b licence.

Is my understanding right or wrong as i am about to book my B+E any day now.