Rob there’s nowt worse than somebody else piling your motor up, but after reading the above I think I must have a say

Firstly the Brakes Failed, the driver stated that, that is his opinion full stop, to hell with his foot slipped off the pedal, why should he make himself look incompetent when his brakes failed?
You say the brakes were piping hot? I would say that is a brake problem, the brakes do get hot with frequent stopping and starting or down hill driving, but you’ve stated he just could’nt stop at the TOP of the ramp after travelling on the M1, this to me sounds like the brakes were badly adjusted and have been heating up through friction whilst driving, I may be an exception, but it’s very rear I need to brake going uphill
the gearbox is used for slowing then the brake for the last few yards if required, this certainly would’nt give enough time to overheat the brakes into brake fade.
Trailer brakes cold? well in my opinion it could be a sign of the trailer brakes not working, but then again, how often had the driver been braking? they only heat up from the friction of being used a lot.
I had a Brand New Seddon Atkison when the old H reg plates came out in the early 90’s, after travelling down hill the brakes went and I hit the back of a bus, immediately it was put down to my fault as nothing was found wrong with the brakes, despite my denials, the truck was only about 3 months old, it was run on a rolling road (Empty) despite being fully loaded at the time of the accident, no problem was found.
About 5 weeks later, the brakes failed on the Sister Truck (Consecutive Reg Numbers) so the Ministry were determined to find out why both trucks suffered brake failure, mine was luckily still away for body work repair so had not been touched mechanically, when the ministry took the wheels off and began looking at the Brake Drums, they were found to have small cracks in the drums, both trucks had suffered from faulty drums which failed when they became hot by expanding away from the brake shoes, the 4 drums on each wheel were the same, the verbal warning I’d recieved was immediately withdrawn and the “Driver Error” retracted.
So in my opinion after my experience, I would say it’s possible that a similar thing had happened with your truck, of course they wont fins a problem when the brakes are cold or it’s run on a rolling road for a few minutes.