Riot squad officers were mobilised to a Midland jail after inmates were involved in a three-hour stand-off with wardens, insiders claim.
Sources say 15 prisoners took part in the disturbance at Hewell Prison, near Redditch, which they say forced the authorities to call in the reinforcements.
Inmates are said to have mounted the protest after blaming staffing cuts for a loss of association time, when they are allowed out of cells to mix with each other.
Bosses at the Category B prison, which has been previously criticised for overcrowding, have moved to play down the stand-off.
But a source said: “The authorities mobilised a tornado squad, which is basically a riot squad of prison officers.
“It was a protest about the loss of the prisoner association time. It’s happening because of staffing shortages. The prison does not have the manpower to supervise the association time.
“Because there are so few officers at Hewell, they were planning to bring in from other prisons to deal with the disturbance. But the prisoners gave up before the extra officers were deployed.
“The tensions inside the prison are extremely high at the moment.’’
A spokeswoman for the Prison Service denied that the protest had been violent and said it had lasted three hours.
She added: “On Saturday September 21 a small number of prisoners at HMP Hewell refused to return to their cells. Prison staff resolved the incident with no injuries to prisoners or staff.”
She added that police were not investigating, but the service did not comment on claims that association time had been cut because of staff cuts.
The prison was criticised for overcrowding earlier this month by the Howard League for Penal Reform.
Chief executive Frances Cook said: “At last, we have the picture of the real state of overcrowding in our prisons. It’s far worse than anyone imagined, one in four people behind bars are packed like sardines into cramped cells.
“It should come as little surprise that such crowded conditions leave staff hugely overstretched, especially as more are being laid off.
“Staff cuts and overcrowding mean men spend all weekend and up to 22 hours a day during the week cooped up like battery chickens – no wonder violence and self-injury is rife.”
But Prisons Minister Jeremy Wright previously said: “Let’s be clear what overcrowding in prison actually means, typically it means having to share a cell rather than have one to yourself. Prisoners are treated humanely but prison is not somewhere that anyone should be comfortable about going back to. All prisons have safe population levels.”
HMP Hewell branded filthy, unsafe and easy target for drugs.