Not unlike the US of A, the United kingdom has a crime problem. A lot of the criminals who are the cause of this problem commit acts severe enough to be sent to prison, which has resulted in the UK prisons getting seriously overcrowded, which in turn entail a great deal of other problems, including a lot of inmate violence, even incarerated children as young as 15 are exhibiting violent behavior towards eachother and their guards. The UK government is considering to let these guards use violence to protect themselves from these "kids".
So, untill they manage to complete a set of superprisons, they needed a quick-fix patch job solution. Long story short, they decided to start letting people out of jail early and sending less people to jail.
The first problem was obvious, if you're simply releasing people to incarcerate others, the prisons will remain overcrowded hellholes, this is hardly a motivator for rehabilitation.
Secondly: What about those released? The parole officers are swamped with work, and a lot of criminals aren't even referred to the probation service! The obvious consequence:
" We warned the government it would happen and it has. ... there have been a number of occasions where men have returned, violence has been committed and the police have been involved. "
And remember, if these people are victimised again, there's a 39% chance it won't even be investigated!