Media playback is unsupported on your device Media caption Speaking to the BBC, one prison officer said: "Wires had been strung up as tripwires at chest level"

A disturbance at a jail described as an incident of "concerted indiscipline" by authorities was in fact a "full-scale riot", a prison officer has said.

England's largest prison, HMP Oakwood, near Wolverhampton, was the scene of disturbances earlier this month.

G4S, which runs the prison, said about 15 to 20 prisoners were involved.

But the officer, who went inside to tackle the violence, told the BBC many more inmates had been involved and they took over an entire wing of the jail.

Some had booby-trapped doorways and were shouting threats from behind a barricade, he told Radio 4's The Report programme.

'Armed and dangerous'

The officer was part of one of the "tornado teams" called in to Oakwood to help deal with what was going on.

The teams are made up of specially trained prison officers, who others can call on when situations get out of control.

Find out more Hannah Barnes's report on HMP Oakwood can be heard on BBC Radio 4 at 20:00 on Thursday, or afterwards on the iPlayer The Report: Oakwood Prison

"Our briefing was that the prisoners were armed and dangerous and that it was a very large number of prisoners and they had completely taken over an entire wing of the prison," said the officer.

He described how inmates had barricaded themselves inside Cedar Wing and were making threats.

"They'd interfered with locks to try and prevent staff getting into the wing and they were destroying everything they could get their hands on. I did hear prisoners shouting threats, saying, 'We're ready for you, come on - we're gonna get you' and words to that effect."

He told the BBC that the wing was "trashed", with debris and iron bars on the floor.

"Wires had been strung as tripwires at leg level and at chest and neck level as well, to try and prevent us from moving in an orderly fashion down the wing and sort of break us as we went through."

"I would sum it up as a full-scale prison riot and we were very lucky that it only took place on one unit and didn't spread."

Media playback is unsupported on your device Media caption Jerry Petherick: Disturbance involved "small number of prisoners"

Home-made alcohol

Jerry Petherick, director of custodial and detention services at G4S, said the prison was sufficiently controlled "with standard procedures".

Answering allegations home-made alcohol could have played a part in the incident, he said drink was an issue for all public and private sector prisons.

"There are many ways prisoners can illicitly brew alcohol," he said. "It's one of those constant features, we search for it, we remove it, destroy it, place prisoners on report for brewing it."

In a statement, G4S said: "The trouble we experienced was concerted indiscipline by a small group of prisoners confined to one wing; it was not an issue affecting the wider prison.

"The reasons for the incident are still being investigated and we will be in a better position to comment on what might have precipitated it after the investigation is finished."

Justice Secretary Chris Grayling has said the site, which has space for 1,600 inmates, is meant to be the blueprint for future prisons.

But last year Oakwood was given the lowest performance rating possible by the Ministry of Justice. Its report was particularly critical of staff at the prison.

"Many staff were passive and compliant, almost to the point of collusion, in an attempt to avoid confrontation, and there was clear evidence of staff failing to tackle delinquency or abusive behaviour."

'Lives at risk'

A prison custody officer from Oakwood also agreed to speak to The Report, on condition of anonymity. He defended his colleagues, saying: "There are some excellent staff there. It's just there are not enough of us.

"I've had comments made to me that people are dreading coming to work - it makes them ill, the thought of coming to work and it's a relationship killer."

But he said that he was put in dangerous situations every day because of the lack of experience of staff and there simply not being enough of them to make the prison function properly.

"There should be two prisoner officers to a wing - quite often you'll find that there is just one officer on his own, dealing with up to 60 prisoners at any one time. There are times when there are no staff at all on the wing, although not for very long periods of time."

New prisons are very difficult to run and set up successfully and... although there are some advantages of scale, big prisons are more difficult to run Nick Hardwick, Chief inspector of prisons

He also said that prisoners' lives were being put at risk and that in some cases, the records showing that inmates at risk of self-harming had been checked up on were being falsified.

"If there is a prisoner who has a potential for self-harming… because of staffing levels, sometimes they just don't get covered as adequately as they should.

"Staff will write up, 'Lying in bed, watching TV...' but he hasn't been checked for the last hour. So they will go and check him and he will still be alive, and then they will lie that he was being checked every 10 minutes for the last hour."

Responding to this allegation, G4S said: "Cases of records being falsified will not be tolerated and any cases identified will be investigated."

The Report has seen official documents which confirm that there has been a reported incident at Oakwood every week from the middle of October last year through to Christmas.

They include serious assaults on staff, cells being left unlocked and prisoners setting fire to the furniture in their cells.

G4S said: "Figures demonstrate that G4S managers at Oakwood have been delivering improvements since the visit of the chief inspector of prisons in June 2013. Levels of violence and incidents at height are reducing and more prisoners are being seen by staff from the offender management unit."

The government claims that Oakwood costs £13,200 per inmate per year, compared with an average of just over £22,000 in similar category prisons.

The chief inspector of prisons, Nick Hardwick, told The Report: "New prisons are very difficult to run and set up successfully and big prisons, although there are some advantages of scale, big prisons are more difficult to run than smaller prisons. So if you have new, big prisons, that's going to be a very difficult job to set up and run successfully."

The Report: Oakwood Prison can be heard on BBC Radio 4 at 20:00 on Thursday, 23 January, or afterwards on the iPlayer