The chief inspector of prisons has voiced fears that inmates may have taken their own lives because they could no longer face life at a violent and drug-ridden jail.
Peter Clarke questioned whether there was a link between conditions at HMP Nottingham and a number of apparently self-inflicted deaths at the jail.
In a highly critical inspection report, Mr Clarke said that for too long prisoners had been held in a "dangerous" and "disrespectful" environment.
He highlighted "tragic" and "appalling" levels of suicide and self-harm at the prison, a category B facility holding around 1,000 male inmates.
There had been eight self-inflicted deaths at the jail since the previous inspection in 2016, the assessment said, including four in four weeks in September and October last year.
While formal causes of death in the cases will be determined at inquests, Mr Clarke said: "My fear, which may prove to be unfounded, is that some could face it no longer and took their own lives."
He concluded that the prison "will not become fit for purpose until it is made safe".
In an unusual step, the chief inspector's warning was echoed by the watchdog responsible for investigating deaths and complaints in prisons.
Acting Prisons and Probation Ombudsman Elizabeth Moody said: "It is highly troubling that HMP Nottingham has a history of failing to implement recommendations from our investigations into deaths at the prison."
HMP Nottingham has been at the centre of concerns over the safety crisis that has hit much of the prison estate in England and Wales.
In the wake of the inspection, Mr Clarke used a new "urgent notification" system for the first time to raise the alarm over the state of the prison.
The report from HM Inspectorate of Prisons said levels of violence were "very high", with 103 assaults on staff in the previous six months.
Over the same period, there had been 198 incidents where prisoners had climbed onto the safety netting between landings.
"This level of disorder contributed to a tense atmosphere at the prison," the inspectorate said, adding that many violent incidents, including serious ones, were not investigated at all.
The prison needed to do "much more" to tackle the problem of drugs which was "inextricably linked" to violence, Mr Clarke said.
In a survey, more than half of inmates (57%) said it was easy to get illegal drugs.
The transition to a smoke-free environment in August was linked to a significant spike in medical emergencies related to synthetic cannabinoids.
Prison intelligence indicated illicit tobacco was sought after and accessible, and that in-cell electrical goods such as kettles were damaged by prisoners attempting to light cigarettes, according to the report.
Inspectors welcomed the installation of phones in all cells at the jail, adding that prisoners could also maintain contact with their families by email.
Michael Spurr, chief executive of HM Prison & Probation Service, set out actions being taken to improve conditions at HMP Nottingham.
He said: "Drug testing has been increased, specialist staff are working with vulnerable prisoners and safety is the absolute priority for the Governor and staff every day.
"We have strengthened management arrangements, are providing external support and will monitor progress closely over the coming months."
The Government said it remained "absolutely committed" to turning HMP Nottingham around.
Justice Minister Rory Stewart said: "Through the new urgent notification process, we have quickly and decisively begun to address the very grave issues at HMP Nottingham."
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