Finally got something!

[ChristiaanV]

Well congrats.
A mini is always a fun (read sometimes F*cken frustrating) car to have.

What is "terrible"? Do you need to pump the pedal before it grips? Does it pull to one side when you brake.

It may be as simple as drum brakes that need to be adjusted

I cannot remember if pumping worked as we had the previous owner drive it to my place. I'm getting into the car deeper after work, probably starting with soaping off from one end before I start opening up.
'terrible' as it does not turn to the side, just triple the stopping distance required even with the brake pedal on the floor.
Maybe I'll pop the wheels off and check the drums before I open the master cylinder.