Prisons in England and Wales are in crisis after "perverse" Government reform and a "toxic mix" of pressures, the head of the body representing governors has warned.
Andrea Albutt, president of the Prison Governors Association (PGA), launched a blistering attack on the Ministry of Justice (MoJ), saying its members had been left "devastated at the complete decline of our service".
In an open letter published as riot officers were called to a prison for a second day, the governor said a recent increase in indiscipline among inmates is "of grave concern".
The Government has said it has taken "immediate action" to increase prison officer numbers while creating a new body to drive through its reform programme.
However Ms Albutt said members had told her that they have seen "nothing tangible" come from the MoJ to ease the burden on prisons, leaving governors facing "unacceptable stress and anxiety" on a daily basis.
"We know many prisons are in crisis and I deliberately use that term, because it can't be dressed up in any other way," she said.
The governor warned an unforeseen rise in prisoner numbers had left the estate with "virtually no headroom" in spaces, while seasonal pressures were adding strain to limited staffing levels.
Specialist teams were called into HMP The Mount in Hertfordshire for the second day on Tuesday after inmates reportedly seized control of part of a wing, while HMP Erlestoke in Wiltshire also saw an incident involving prisoners.
"The instability we are seeing is clearly linked to a poor regime," Ms Albutt said.
"Further loss of accommodation, like those lost during the current, ongoing incidents at The Mount over the last couple of days, means drafts of prisoners are being moved across the country, compromising the Families Pathway and destabilising the receiving prisons as they try to maintain order amongst disaffected displaced men.
"This toxic mix does not have a quick fix and the future looks like more of the same."
The governor said the issue of prison officer recruitment remained "critical", with a net increase in the number of prison officers in 2016/17 of just 75.
However she also raised concerns that a drive to increase the number of officer numbers too rapidly may cause further issues.
Members of the PGA have warned that the selection process was allowing "many unsuitable people through" while training was of "poor quality".
As part of its reform plan the Government has split operational control of offenders from policy decisions, with Her Majesty's Prison and Probation Service (HMPPS) taking the place of the National Offender Management Service (Noms).
According to the PGA there are currently 40 "prisons of concern", of which 10 are "very concerning".
A spokesman for the MoJ said: "We know that our prisons have faced a number of long-standing challenges, which is why we have taken immediate action to boost prison officer numbers and have created Her Majesty's Prison and Probation Service.
"This will help to create a distinct, professionalised frontline service and will ensure that policy and operations are working closely together to deliver these much needed reforms.
"We need to create calm and ordered environments to help ensure effective rehabilitation, and we continue to work closely with the unions and all staff to help achieve these vital reforms and make prisons places of safety and reform."
Tory MP Bob Neill, Justice Select Committee chairman, said the bigger problem was a serious disconnection and growing lack of confidence between "the top brass, if you like, of the Prison Service and the operational people on the ground".
Mr Neill also told the BBC that low staffing was an issue, alongside a failure to hold on to more experienced employees.
Shadow justice secretary Richard Burgon said Ms Albutt had confirmed the "deep crisis" in the country's prisons, adding: "Prisoners are not being rehabilitated and this is putting the public at risk."
Conservative Sir Edward Garnier, formerly solicitor general, told BBC Radio 4's World At One: "It is true to say that there are probably not enough prison officers.
"But the problem is really to be found in overcrowding and until this Government or any future government breaks the back of overcrowding, we're going to have this constant revolving door problem of disturbance in prisons, dissatisfaction amongst governors and prison officers, dissatisfaction for... the prisoners, and unsatisfactory results for the public at large."