Definitely a reporting case....the problem is, if you don't and help this cat then the "official channels" have no knowledge of how badly the owners care for animals and no further check ups will be done.
I'm currently feeding a cat on our road, and have reported it's owners to the RSPCA. She's always out and she comes to our door for food. She's also had BIG scabs on her that have obviously been left after they happened and will try and bite if you touch certain parts of her body, as though it hurts. My theory is if anything's said to me I can say "how stupid do you think I am? To feed your cat really obviously AND report you....?"
Poor thing, sounds like it gets no social interaction whatsoever.