A prison officer could be killed by an inmate during violence sparked by soaring temperatures during the current heat wave, the government has been warned.
The warning was delivered by the Prison Officers Association (POA) to justice secretary Chris Grayling, following a riot at HMP Ranby in Nottinghamshire last weekend.
Conditions inside cells have been described as being like an 'oven' during the spell of hot weather in England.
Tensions are reaching boiling point as inmates spend hours inside small shared cells and 'association time' is cut due to staffing shortages.
It is feared that these conditions will present a perfect storm for disturbances to erupt, with prison officers the number one target of inmates' aggression.
At HMP Ranby in Nottinghamshire, 120 inmates went on the rampage after refusing to return to their cells after association time. A fire was started during the disturbance, but no injuries were reported.
Following the incident, more riots at other jails have been predicted.
Steve Gillan, general secretary of the POA, blamed disturbances like that at Ranby on a combination of prison closures, staff redundancies and the increasing prison population.
He told IBTimes UK: "All the ingredients are there for the perfect storm, but it's falling on deaf ears. If they [the government] do not take heed, then I think we shall have on our hands the death of a prison officer.
"We are seeing massive increases in serious assaults on our members, self-harm by prisoners and also prisoner on prisoner attacks. It is down to the professionalism of our members that they have kept the lid on things so far, but we've come exceptionally close to seeing prisoners killed."
Being locked up inside a cell during hot weather can be one of the factors involved in bringing inmates to riot, according to a firm which advises convicts on how to handle life behind bars.
"Cells become ovens very quickly," said Steve Dagworthy of Prison Consultants. "You can't open your door or window. It's like torture being locked in a box 23 three hours a day.
"Imagine being in a 12x10 cell with another person and a tiny window and you get half an hour to have dinner and that's it" said Dagworthy, who served time in prison himself. "Inmates get to the point where they say 'you [prison staff] are treating us like dogs' and if you treat someone like an animal, they will go feral."
More prison riots were predicted by both Gillan and Dagworthy in the coming weeks and months, as Britain enjoys high temperatures and blistering sunshine. The country sweltered in a heat wave last week, with record highs recorded for the year.
Staff shortages were blamed for the riot at Ranby by Labour MP John Mann, who claimed "it's clear prisoners have been running the prison.
"There are not the numbers or the expertise among the staff to deal with [trouble]. The governors were warned, the Government was warned, by me and by many others, that this would lead to disaster."
IBTimes UK contacted the Ministry of Justice. A spokesman said there was "no crisis" in UK prisons.
"We have taken a number of appropriate steps to ensure we can safely manage the recent rise in the prison population, including re-opening reserve capacity and an ongoing staff recruitment drive, which includes the establishment of a reserve force of former staff who can be called on when needed," he said.
"These are sensible and proportionate measures to ensure we can respond flexibly to any demands."