A dramatic rise in violence at a prison in Warwickshire has left it no longer safe for inmates, the chief inspector of prisons has said.
A scathing report into the conditions at HMP Onley found there had been a significant decline in standards over the past four years, including a tripling of assaults behind bars.
The number of prisoners self-harming had also increased significantly, inspectors said, while a shortage in prison officers left inmates being let out of their cells for as little as three hours a day.
Staff told inspectors the rural prison had faced significant challenges after previous government reforms introducing so-called resettlement prisons had forced it to take inmates from London, bringing with it the city's gang-related violence.
"In our survey, far more prisoners than at similar prisons and than at the time of the previous inspection said that they felt unsafe," said the HM Inspectorate of Prisons report, published on Friday (2 December).
It added: "Since it was last inspected in 2012, it had been designated as a resettlement prison for Greater London, which undoubtedly had a significant impact on the prison in terms of the changed nature of its population."
The adult male prison, near Rugby, made headlines over the summer after video footage emerged online showing a prisoner biting off the head of pigeon as part of a gruesome stunt to get drugs.
Inspectors found when they visited HMP Onley in July and August that more than half of prisoners said it was easy to get hold of illegal drugs, including new psychoactive substances like "spice" that have contributed to the surge in violence.
Other clips from the Category C prison – taken illegally by inmates on smuggled mobile phones – showed fighting between rival gangs outside cells.
Prison officers complained staff cuts had affected their ability to manage inmates.
Peter Clarke, chief inspector of prisons, said there was "a clear need for the leadership of the prison to get a grip of the problems facing them". But he added: "Of course staff shortages have had an impact on many areas of service delivery, but they did not offer an excuse for a decline in standards of the severity that we found."
He said more analysis needed to be done to determine the cause behind the rise in violence.
HMP Onley was originally built as a borstal in 1968. At the time of the inspection it held around 740 prisoners, two lower than its operational capacity.
Frances Crook, head of the Howard League for Penal Reform, suggested it had been badly affected by its reclassification as a resettlement prison for London, saying it came amid "muddled" reforms brought by previous ministers that had "conspired alongside the staff shortages to bring violence and instability to Onley".
The report comes as the prison service suffers record levels of violence and self-harm due to a toxic mix of overcrowding and staff cuts.
Last month up to 10,000 prison officers staged a walkout in protest at the conditions behind bars, saying the prison service was unsafe for staff and in "meltdown".
A string of high-profile incidents – including an audacious prison escape at HMP Pentonville and rioting at HMP Bedford – have piled pressure on Justice Secretary Liz Truss to quicken the pace at which the government's prison reform programme is implemented.
Michael Spurr, head of the National Offender Management Service (NOMS), said in response to the HMP Onley inspection: "As the Chief Inspector points out, there is much good work being done at Onley but the deterioration in safety is unacceptable and reversing this is the Governor's top priority.
"Additional staff are being recruited to meet the commitments set out in the Prison Safety and Reform White Paper and the Governor will use these additional resources to drive forward the improvements required."