Earlier quoted context omitted.
Many, many people in jail were severely mentally ill. There was no support for them. So UK is getting as bad as the US? Or has it never been good over there? Given how mental health conditions and incarcerations (for whatever reason) go hand in hand, I'd expect any sane society to tackle the former even more ferociously than the latter.
Ever since the mental health institutions were mostly shut down in the 1970s and 80s, and the focus for treatment of criminals with mental health problems became "care in the community", the UK prison system has become a dumping ground for mentally unwell people. See http://www.sciencemuseum.org.uk/broughttolife/themes/menalhe... .
Note that my father was among the people who took early retirement in disgust at the way things are going, so my views are almost certainly coloured by that.