Staffing levels in many jails are too low to maintain order and run a decent regime, the prisons watchdog has warned.
In a scathing critique, Peter Clarke said he had often been "appalled" by conditions in which inmates are held.
Mr Clarke, Chief Inspector of Prisons in England and Wales, highlighted the prevalence of drugs behind bars, saying the "seeming inability" to keep them out has been a major factor in declining safety standards.
Too many prisons still lack an adequate strategy to tackle drug supply, his assessment said.
Inspectors had seen many inmates who were "obviously" under the influence of drugs during visits.
Mr Clarke's annual report for 2016/17 said debt, bullying and self-segregation by prisoners are commonplace.
"This has all been compounded by staffing levels in many jails that are simply too low to keep order and run a decent regime that allows prisoners to be let out of their cells to get to training and education and have access to basic facilities," he said.
"When a person is sent to prison, the state accepts responsibility for their well-being, including their physical and mental health, safety and education. There is clear evidence that for too many prisoners, the state is failing in its duty."
Staffing levels have repeatedly been highlighted as violence and self-harm surged to record levels across the estate.
Assaults on staff jumped by 38% last year to 6,844 incidents.
At the height of the crisis last year, there were a flurry of disturbances.
Of the 29 local and training prisons inspected during the year, inspectors judged 21 of them to be poor or "not sufficiently good" in the area of safety.
Mr Clarke criticised "squalid, dirty and disgraceful" conditions in some establishments.
Far too often, men are sharing a cell in which they are locked up for up to 23 hours a day, his report said, adding that on several occasions, prisoners pointed out insect and vermin infestations.
Mr Clarke said that in many cases, the response to his inspectorate's previous recommendations has been "unforgivably poor".
The number of recommendations that had been fully achieved was lower than the number not met for the first time in 2016/17.