Staff at Britain's most violent jail arranged brutal fights between rival gangsters, according to a decorated former prison officer.

Peter Hiett claimed inmates at Feltham Young Offenders Institution were ushered into cells padded with mattresses for fist-fights, in scenes resembling the 1999 film Fight Club, starring Brad Pitt and Edward Norton.

The Ministry of Justice (MoJ) has denied the claim, but Mr Hiett told the Sunday People: "It was like a sport for them. If two inmates had a grudge they’d put them together in a room to sort it out.

"They would pad it out with mattresses and gym mats so nobody got really hurt.

“They only stopped when one was knocked out or couldn’t defend themselves any more.

"Some guards watched; some turned a blind eye to it.”

Feltham Young Offenders Institution

Mr Hiett, 49, was commended for bravery during his eight years working at the prison, in Bedfont Road, where he also said he once reported an officer for having sex with a teenage murderer in his cell.

But he said officers were afraid to visit certain areas during his time there, as gangs controlled entire wings of the jail.

He said: “The managers thought it would be a good idea to house all the members of each different London gang on a separate wing.

“So you would get large groups from, for example, the Mandem crew, or the DSN (Don’t Say Nothing) gang, who would hang around together.

"There would be 15 or 20 lads from the same gang on the same wing. They would protect each other, deal drugs.

“And if they saw another gang member all hell broke loose. Their wars don’t stop when they’re behind bars.”

He added: "Once I was escorting a 17-year-old inmate with just one other female prison officer when we were attacked by a gang of 30 inmates – two of us against 30.

“I was trying to unlock a door as they ran towards us. I couldn’t open it in time and they smashed us to pieces. I had to go to hospital for my injuries.

“This was a regular occurrence. Huge group assaults on a rival gang member being escorted around the prison by just one or two officers.”

Whistle-blower: Decorated former prison officer Peter Hiett

In another startling accusation, Mr Hiett, who claims he was forced out of the Prison Service in January last year for whistle-blowing, said management fiddled assault figures to hide the true level of violence at the prison and to meet targets – a claim also denied by the MoJ.

He said that in 2012 senior management established a so-called Behaviour Management Group (BMG), a working party made up of ten prison officers, set up specifically to fiddle the assault figures.

He added: “It was made up of hand-picked officers. A common tactic was to treat group attacks as one ­assault.

"When 22 people attacked one person only two were charged – and not with assault, just ­endangering health and safety.

"It should have gone in the books as 22 separate assaults – but they didn’t want the truth about the amount of violence to get out.”

Mr Hiett claimed he raised his concerns through internal channels several times, before finally approaching Jeremy Wright, who was then Minister for Prisons and is now the Attorney General.

In 2013, Mr Wright inspected the prison with senior aides and launched an internal inquiry. Independent adjudicators were then brought in to look at the recording of assaults.

But Mr Hiett said: “Very little changed. The whole system needs to be overhauled."

Senior Labour MP Michael McCann added: “The circumstances that Peter Hiett describes are worse than those depicted in the 1979 movie Scum."

Last year, the Howard League for Penal Reform named Feltham as the most violent prison in England and Wales. Staff levels fell from 403 in 2010 to 280 in 2014.

An MoJ spokesman said: “It is completely untrue that staff at YOI Feltham are complicit in any acts of violence within the establishment.

“It is also untrue that figures relating to incidents at Feltham are in any way altered.”