As another Old Labour supporter, I would support most of what has already been said, and add that Scandinavia, France and Holland have a much more humane - and constructive - prison regime, and none of them imprison the proportion of the population that this country does, nor do they have anything like the same rates of reoffending - so 'broad arrows, porridge and breaking rocks' are not the only way to reduce serial offending.
I'd add the argument that what makes British prisons more horrific than anything is the extent to which they are notorious cesspits of an anarchic subculture imposed by the inmates, not by the staff - this because staffing, security etc are so underfunded and inadequate.
We should look first at what has gone wrong with contemporary Britain to cause so many to commit imprisonable offences - then look at establishing a much more supervised, disciplined but positive and reforming regime for those who continue to be sent to prison - a regime they would probably fear much more than the present shoestring, ramshackle anarchy that is the result of government by misers on behalf of millionaires and mutinationals.