Down my road a disabled lady had a disabled parking space marked out in front of her house. At some point she had a run-in with the man across the road over parking. He then started to park in her space. Obviously she complained to the council, but he had apparently done some homework and discovered that legally there isn't a thing anybody can do to stop him.
Prior to the argument with the lady, he'd been putting out cones and a dustbin to mark out a parking space for himself, but the council put a stop to that. Just a few days ago I watched his wife park in the disabled space, with no cars for 100 yards in either direction. I generally leave others alone when it's none of my business, but it does make me think about doing something sometimes.