It goes back to people like Elizabeth Fry. She might not have used quite the same terminology, but the concept of rehabilitation was definitely there. She was sufficiently important in this field that she's on the back of the five pound note.
Thanks for the reference, Steve. I had heard of Elizabeth Fry, but had never had her role in society explained. Having looked her up, she was clearly a strong-willed woman who was willing to stand up and declaim things she felt were wrong. It's not yet 10:00am and I've learnt something important, so again, thanks.
However, (you knew that was coming, didn't you?) her main focus seems to have been the health and welfare of (primarily) women prisoners and the conditions in which they were incarcerated. That these conditions were improved is clear. It's also clear that such progress was very slow. This, though is not what we mean when we talk about "rehabilitation" today, is it? Nowadays, rehabilitation means (roughly) "restoring a criminal's character so that he can return to become a contributing member of society." My own view is that prisons are almost uniquely incapable of performing this function. (How can you make someone 'fit for society' by locking them away from society?) It is clear to me that this was not a historical role of prisons and I don't know when it was imposed on them. My guess is post-1945.
I realised, while typing that paragraph, that my views could be misunderstood (as always). While I do advocate a return to a "harsher" prison climate, I do not advocate a return to stone-flagged floors, straw to sleep on and a bucket in the corner. I simply don't accept that prisoners should have levels of comfort which are beyond the reach of many law-abiding citizens, such as some pensioners.