Prison Overcrowding

Heard something on Radio5 today about our overcrowded prisons and "what can we do about the situation?" Seems to me a very simple equation - if the prison population is rapidly increasing, custodial sentences obviously aren't working as a deterrent. If a prison sentence was genuinely harsh, criminals would be alot less willing to re-offend. Make the conditions as hard as possible and you at least wouldn't get the homeless committing petty crimes to get a roof over their head, with a bed, central heating and three square meals a day. I regularly see reports in the local paper of this sort of thing going on, and you can't really blame them either, if they're stuck sleeping outdoors in the middle of winter. It proves the point about prison conditions though. Bring back hard labour, or at least make a prisoner earn his keep. Privileges shouldn't be televisions and hi-fi's, they should be heating and decent bedding. If a spell inside was the worst experience of your life, you're not going to consider doing anything that might land you back there in a hurry.
Lest I be thought some sort of stone-age rightwinger, I'll add that on a related point I'm hugely offended by what's going on at Guantanamo Bay. Detaining people indefinitely without charge is what military dictatorships do, and it has no place in democratic societies whatsoever. It's a massive evil stain on the self-proclaimed "Land of the Free" and makes a mockery of everything they're claiming to defend.
The difference here to my mind is that a UK prisoner has been tried and found guilty, and though no justice system is perfect, the majority of cases are presumably pretty sound. Hence a convict has forfeited his right to decent treatment by society and needs to understand that actions have consequences. If they don't like the consequences they need to change their behaviour. If they're not too bothered by the consequences (comfortable cell, free food, etc.) why bother changing their behaviour? The kidnappees at Guantanamo Bay have, on the other hand, been rounded up on the flimsiest of suspicions, are denied access to the law and are essentially political hostages.
So I'm not at all right-wing by inclination, but even I can see the "caring, sharing, rehabilitation" approach simply isn't working in the UK and we're reaping the results of too many years of sociologists' theories rather than real-world experience.