All brakes binding, rear lights on

[Goran]

Hi all, I hope you are all well, I have been away for a while.
I drove my 8 to a MOT test today, so exciting to drive it after its been sitting for a few months.
I passed the MOT, and promptly all my brakes failed


As he hands me my keys the MOT guy tells me “your rear brakes are binding a bit, do you live far”
Then he tells his colleague “I need a cup of tea after this one” 😂
Sure enough when I try driving the car out of the industrial estate the brakes are dragging, by the time I make it to the entrance of the estate the car will barely move in 1st gear at 4000 revs.

All 4 discs are hot and the brakes smell. The rear lights are on constantly and the brake pedal is slammed to the floor, rock solid.
I got recovered on a flatbed to my local mechanic. The RAC guy tells me he thinks the mot tester must have stomped on the brakes too hard.

I’m guessing its the master cylinder?