Riot police sent in after disorder at The Mount jail
Riot police had to be sent in to quell trouble at a jail that has struggled with "severe" staff shortages.
Multiple prisoners were involved in a lengthy disturbance across two wings at HMP The Mount in Hertfordshire.
The incident came on the same day as a report warned the prison had lost experienced staff and last summer suffered problems including violence.
The Ministry of Justice said the incident, which began on Monday afternoon, was resolved shortly after 10pm and no staff or inmates were injured.
The so-called Tornado squad, equipped to deal with riots, was sent in while police vehicles were pictured at the prison and ambulance crews and fire engines were also seen at a former airfield close to the jail.
One commentator described the prison as having been "on the brink of a meltdown" in the run-up to the disorder.
Recent weeks have seen some inmates locked in their cells all day, with cold food delivered to their cell doors, prison affairs academic and blogger Alex Cavendish said.
A woman who said her son is an inmate tweeted during the disturbance: "My son is at The Mount he has been on 24 hour lock down for weeks."
Mr Cavendish said he had also heard complaints of prisoners not being allowed out to shower or make phonecalls.
He said: "The technical term is that the staff have lost control of two wings. What 'lost control' means is that the prisoners are basically rioting, in layman's terms."
A Prison Service spokesman said: "Specialist prison staff resolved an incident involving a number of prisoners at HMP The Mount on Monday evening. There were no injuries to staff or prisoners.
"The offenders responsible will be referred to the police and could spend longer behind bars."
An assessment from the jail's Independent Monitoring Board (IMB) said that last summer "all the ingredients were in place for The Mount to suffer disorder such as has been experienced in other prisons - staff shortages, readily available drugs, mounting violence".
The report covering the 12 months to the end of February said that during the year The Mount has struggled with staff shortages "driven by uncompetitive pay scales".
It said: "Experienced staff have left and not been fully replaced, so that at the end of February there were 24 vacancies out of a complement of 136 officers, and a high proportion of officers and managers had less than two years' experience."
Despite the shortages the IMB said the establishment ended the year as a safe prison where prisoners have a good chance of rehabilitation, with the governor and staff managing to control violence.
It said the drug problem at the jail was most acute in November when a number of prisoners suffered serious short-term health problems with 70 emergency call-outs in the month, mainly for drug-related problems.
The substance known as Spice is a "big concern", the report said, adding that while drone deliveries have declined, "the supply is still getting in".
The Category C male prison, which opened in Hemel Hempstead in 1987, has a population of more than 1,000 prisoners.
The facility is described as a "hybrid training and resettlement prison" which caters for a number of inmates nearing the end of their sentences who are residents of the county and nearby areas.
Campaigners and watchdogs have issued a catalogue of warnings about violence, drug use and overcrowding across the prisons estate in England and Wales, which has been hit by a number of disturbances in the last year.
Last month Peter Clarke, the Chief Inspector of Prisons, warned staffing levels in many establishments are too low to maintain order and described the conditions some inmates are held in as "squalid, dirty and disgraceful".
Mark Fairhurst, acting national chairman of the POA - the Professional Trades Union for Prison, Correctional and Secure Psychiatric Workers - said staffing issues at jails are a national problem.
He said: "It's an epidemic throughout the country and we've been telling the employer for years now that they need to sit down with us and restructure the whole salary scales.
"They are just not competitive enough with other public sector bodies or private industry.
"So we need to increase the starting salary to incentivise people to join and then we need to give them regular increments to incentivise them to stay. That's not happening at the moment."
Asked why it is difficult to retain staff he said: "It's a combination of adverse working conditions, the violence that they face, and the poor salary."