Prisons exist to protect the public and to help offenders turn away from crime. Every year thousands of criminals are jailed in London and thousands are released. So what really stops people re-offending once they're out?
Ria Chatterjee spoke to one former prisoner, a man convicted of manslaughter and served time. He claims the key to rehabilitation is mental health support.
While behind bars he says he received none and on release was offered none.
This lack of support, he believes, is why criminals go on to re-offend. London offenders aged between 18 and 20 have the highest re-offending rate in the country.
Ria Chatterjee: You're able to reflect, share your story and think about your experiences - how does it sit with you - the person who's not here anymore - can't do that?
Ria Chatterjee: Did it ever for you get to a point where it felt normal to be inside?
Ria Chatterjee: Do you think currently there are very young people entering the prison system who aren't necessarily being rehabilitated in prison and maybe coming out in their twenties and potentially going back into that same cycle?
Ria Chatterjee: What do you think needs to be happening in jail to make rehabilitation more successful?
Ria Chatterjee: And what would you say to people who say the reasons haven't got anything to do with it - an individual makes a choice, they make that choice themselves and it's within their own power whether of not they choose to steal something from a shop or pick up a knife?
Ria Chatterjee: Did you receive mental health support or therapy when you were in prison?
Ria Chatterjee: Would you have wanted that?
Ria Chatterjee: At the time you feel like you wouldn't have had therapy because it felt alien. Do you think that's something a lot of young men would relate to, this idea of I'm not sure about talking about my feelings?
Ria Chatterjee: Why would it help?
In a statement the Ministry of Justice said increased support was available to vulnerable offenders - especially during the first hours and days in custody - and more had been invested in mental health awareness training for prison officers.