So after a visit to the local VW garage, this is what the experienced sales guy said:
When reversing down a gradient, slight or otherwise, with the autohold on, the computer thinks that the car is 'rolling' down the hill. so it quickly brakes all four wheels to prevent this. This is despite having the car in reverse gear and lifting the clutch up and with a small amount of throttle, which I understand, should disengage the autohold (but didn't last night!).
He believes the braking computer system, gets confused and therefore brakes the car when reversing down a slope, unnecessarily. He also said he thought it best to take auto hold off, before reversing downhill/slight slope again.
So what do think guys? All I know is that I forgot to take autohold off tonight, when reversing into the same space, on the slope and no problems tonight! No baked brakes, nor cooked clutch!