I was turning into my driveway and bumped the kerb slightly, so I put the car into reverse to straighten up, however, the brakes would not slow the car down and it started rolling down the hill.
It felt as though I had pushed the brakes in fully, even though they weren't depressed very much - i.e. the brake pedal felt really solid.
I put the handbrake on and eventually stopped the car, but not in time to stop it hitting a car that was parked on the side of the road.

In retrospect, I should have just stalled the car and put the brake on sooner, and tried steering it clear of the car, but I guess I just panicked.

I don't think the bump into the kerb was significant enough to mess up the wheel alignment, so does anyone have any idea as to what caused this?

 

Not up on the S40, but my thoughts are;

Solid brake pedal with little to no actual braking force, to me suggests that the first thing to look at would be brake master cylinder and associciated vacuum line.
Other possability could be a complete catastrophic failure of the ABS, although this to me would be a loooong shot.

I would be amazed if the curb bump has anything to do with this.

In any case I would not move the car until looked at and fixed.
Brakes I do not skimp on.