One of Britain's most famous jails is rat-infested and overcrowded, with prisoners spending most of their time holed up in squalid cells, a scathing inspection report revealed.
Safety has deteriorated at HMP Wormwood Scrubs in London since a previous probe raised serious concerns, watchdogs said.
Inspectors found many prisoners spent all day, and ate "unappetising" meals, doubled up in a dirty, damaged cell with an unscreened toilet.
Some had resorted to improvising a toilet screen with a torn sheet and stuffed paper in broken windows to "keep out the weather", the report said.
Two prisoners deemed to be at risk of suicide or self-harm were found to be in cells in which jagged glass remained in a broken window.
It was a struggle to get clean clothing and bedding, while the jail had a "significant" rat problem, the HM Inspectorate of Prisons report said.
"We saw them every day and night we visited the prison and a large rats' nest was very obvious in the grounds," it added.
Most prisoners had less than two hours a day out of their cells and more than half of the 1,258 men held were locked behind their doors during the working day.
One in five prisoners told inspectors they felt unsafe, with the number of assaults on inmates and staff double that at similar institutions.
Some prisoners were too frightened to leave their cells.
Wormwood Scrubs, which is in Hammersmith and Fulham, was built between 1875 and 1891.
Last year it was claimed that conditions had prompted one staff member to say: "I wouldn't keep a dog in there."
Publishing the latest report, Chief Inspector of Prisons Peter Clarke said: "Wormwood Scrubs is a prison that continues to fall short of expected standards, and at the time of our inspection there was little cause for optimism."
Juliet Lyon, director of the Prison Reform Trust, said: "This shattering report on London's best-known Victorian jail reveals levels of Dickensian squalor which ought to have been consigned to the history books."
Frances Crook, of the Howard League for Penal Reform, said it was "another terrible report", adding: "We cannot go on cramming more and more people into jails without any thought for the consequences."
Shadow justice minister Jo Stevens said: "This shocking inspection report raises huge questions about the Ministry of Justice's competence to address the worsening Tory prison crisis."
Michael Spurr, chief executive of the National Offender Management Service, described Wormwood Scrubs as "an old, crowded, Victorian prison".
He said: "It is challenging to run and we have struggled to make the improvements necessary to meet inspectorate recommendations and to provide a purposeful regime for prisoners.
"Since the inspection, the prison is cleaner; more prisoners are going to activities; violence is being tackled; and better support is being provided to vulnerable prisoners.
"There is a long way to go - but the prison is moving forward and the governor will receive the support he needs to accelerate progress."
The Government previously announced plans to close old Victorian jails and build nine new prisons.
Only HMP Holloway in North London has been confirmed as facing closure so far.
A Ministry of Justice spokeswoman said: "As the Prime Minister and Justice Secretary have said, our prisons are in need of reform.
"That is why we are investing £1.3 billion to transform the prison estate over the next five years, to better support rehabilitation and tackle bullying, violence and drugs."