An undercover reporter has unearthed evidence of intimidation and corruption at a privately-run prison, a Panorama investigation will say.
The reporter, who worked at Rye Hill, a category B prison in Warwickshire, for five months, says prisoners openly threatened a newly qualified officer.
He also says he was asked by inmates to smuggle in mobile phones and drugs.
GSL, which runs the jail, said inmates' behaviour was unacceptable but accused the reporter of ignoring his training.
Murder in cell
HMP Rye Hill is one of a growing number of private prisons in the country intended to help deal with a rising prison population.
It houses 600 prisoners nearing the end of sentences of at least four years, including criminals from the Iranian embassy siege and Strangeways prison riots.
However in the last two years, there have been one murder and two suicides, and government inspectors have given it two damning reports.
During one inspection, prisoner Wayne Reid was stabbed through the heart in his cell by two other prisoners, both with criminal records for violence and knife crime.
Chief Inspector of Prisons Anne Owers said even before the murder, her team had "established to their own satisfaction that they felt it was unsafe and unstable for both prisoners and staff".
As part of the investigation by Guardian Films on behalf of the BBC, the reporter, a former SAS ex-British Army soldier, undertook a 13-week training period to become a newly qualified prison officer.
He was earning £250 a week - a third less than officers in the state sector.
During his time on the wings, he said a new recruit was threatened for enforcing prison rules too keenly.
At one point, she was threatened with a pool cue by one prisoner, the programme says.
The officer said: "I'm not feeling safe because of the staff.
"And I don't know if I can be bothered with it for the money. They're going to kill me I do believe."
GSL's director of communications, John Bates, said: "People shouldn't be surprised by the fact that prisoners in a prison seek to coerce staff into making their lives easier and we don't hide from that fact, and that's why during the training, we return to that theme regularly."
And of the officer, he said: "She shouldn't be frightened. She's fully supported."
In another incident, the undercover reporter says he was openly approached by inmates seeking to "groom" him into a smuggler.
He reports being offered £200 for a standard mobile phone and up to £750 for a camera phone, to be paid to him by telephone banking.
Another prisoner offered him up to £1,500 - more than he earns in a month from GSL - for one delivery of cannabis.
Mr Bates said the prisoners' behaviour was "completely unacceptable" and the reporter knew what they were doing was illegal.
"If that officer had done what he had been trained to do - that matter would have been dealt with. He failed his colleagues and he put himself at risk," he added.
Panorama: Life Behind Bars can be seen on BBC1 at 2030 BST on Monday 16 April