I've been watching this with interest and I'm seeing a lot of misinformation and some misunderstanding. Hopefully this post will help.
As I passed my test prior to 1997 then I find:
Quote from Gov.uk
"If you passed your car test before 1 January 1997 you’re generally entitled to drive a vehicle and trailer combination up to 8,250kg MAM."
So I can use my Discovery 4 (rated to 3.5te) to tow my braked trailer, rated to 3.5te, with a full load on the trailer.
It is only a 'recommendation' to tow not more that the kerb mass of the vehicle.
My trailer brakes beautifully and I need no more 'push' on the car's brakes than without the trailer on. The only problem can be on a continuously long downhill section when the trailer is continuously braking while the vehicle is using engine braking. That does lead to very hot trailer brakes