The British prison system became increasingly chaotic during the 1980s, culminating in the notorious 25-day riot in Strangeways prison in 1990. The response was a five-month public enquiry led by Lord Woolf that prompted major reform throughout the prison system.
Perhaps the most important single change was the introduction of the Incentives and Earned Privileges scheme. Woolf recognised something that seems obvious in hindsight - prisoners on a bread-and-water regime have little incentive to comply with prison rules, because they have nothing to gain and very little to lose. Offering small luxuries like the right to wear your own clothing, access to a games console or a small amount of discretionary spending gives prisoners the opportunity to make rational choices about their own circumstances.
In 2013, the Conservative government made the catastrophic decision to "toughen up" the regime and withdraw parts of the IEP scheme, while also cutting prison expenditure and staffing ratios. The results were entirely predictable - a huge increase in prison violence and disorder.
https://en.wikipedia.org/wiki/1990_Strangeways_Prison_riot
http://www.doingtime.co.uk/how-prisons-work/how-do-prisons-a...