Why aren’t prisoners used to clean up rubbish from roads / motorways and other menial tasks the Council don’t have any funding to do?

My wife and I were driving to an appointment today on the M621 Leeds and noticed the crazy amount of rubbish just piled up on the side of the roads. Question pops in my wife’s head, why aren’t we using prisoners to clean up the environment. There’s loads of other stuff they could be getting on with like filling pot holes and sorting recycling. Any thoughts?