As I remember it, Peter, it was a third OFF for good behaviour. That is, you did two-thirds inside and were only let out early if you behaved. Now you can misbehave all you like and are let out automatically at the halfway point. Governments have been keen to keep people out, not bang them up for longer.
As for prison not working, it depends what you mean. If you mean it does not work because of the high rates of recidivism then you’re probably right. But then you have to have a little regard for cause and effect. Most people who reoffend do so because they are inclined to criminality, not because they’ve spent time in prison. If they were not so inclined they probably would not have ended up inside in the first place. The one way it certainly does work is that it gives the rest of us a brief respite from prisoners’ criminal activities.