Car has failed MOT on brake problem but all.

Car has failed MOT on brake problem but all brake pads have been checked and are satisfactory and the repair garage state the calipers are satirsfactory. They have replaced the master cylinder and have bled the brakes but still state the brake pedal soft. I informed them that some weeks prior to the MOT I kept hearing a brief metal grinding sound as I released the brake pedal when pulling away from my parking spot. This kept happening when pulling away and then one day the noise wasn't there anymore but when I needed to stop, it felt as if the brakes weren't going to work, so kept braking well ahead just in case they were not efficient. In view of this, could it be possible for some small part which was grinding beforehand, had later fallen off? Has this been known before and what part could it be.
Many thanks as my car has been stuck with the repairer for 2 weeks now and I need it. So far has cost over £200 (as in England). Regards Elaine