At risk of veering off topic:
Agreed that I want criminals out of circulation, even if it is on a temporary basis.
From my limited experience, prison seems warm & dry, with nice food and big TVs and pool tables etc., all at the law-abiding taxpayers' expense.
Prison should be a carefully considered blend of punishment and rehabilitation, factoring in a debt to society. For example, while there are thousands of people in jail for non-violent crimes, there shouldn't be any litter in our public spaces. Companies should be able to apply for prison labour to cover manual unskilled jobs, e.g. sweeping out a grainstore.
People who end up in front of the magistrates and get fines, but have no means to pay their debts should have an hour or two in the stocks on a Sunday morning.
I can tell you that prisoners have a number of freedoms, some are however, limited. You will have a hard time convincing the human rights brigade that prisoners should not have access to telephones. This is the UK, not North Korea.
Debt to society is a myth. There is no way you can equate some crimes against society with some kind of debt. I agree that prisoners should be offered the chance to work for money, but if you are equating the prison system with money then you will face the same problems it already has today- not enough investment or money to operate or expand or upgrade.
It is very much in the interests of society that people are houses in the prison system. Firstly, because if they are in prison they can't harm society any further. Secondly, it is by far the cheapest way to keep someone when you consider the costs of some of the alternatives.
I would be in favour of any prison system that keeps the people contained within it easy to manage and which rehabilitates some of them. They should be offered education and healthcare and all the assistance that society can offer because a portion of them will leave and become useful citizens.
We should also consider that a number of the people in the UK prison population are probably there because they are victims of circumstance and have made poor individual choices. Not because they are inherently evil or crooked or the like.
There is no way of adequately punishing someone who has committed the most heinous crimes.