Jimmy Boyle saw his opportunity. He reached across the table and felt the crack as his fist connected with the jaw of the warden of Barlinnie Prison. Within moments the guards were on top of him.

Boyle’s behavior behind bars, where he was regularly involved in riots and attacks on prison guards, earned him the title of Scotland’s most dangerous man.

But his life changed after he was placed in Barlinnie’s experimental – and highly controversial – special forces unit.

The former gangster enforcer, who became a respected sculptor and novelist, has spoken about his experiences as part of his a new BBC Scotland documentary telling the story of the 142-year-old prison, which is about to be closed.

Boyle served 14 years for the 1967 murder of gangland opponent William ‘Babs’ Rooney.

He has always denied committing the murder.

During his early incarceration, he waged a one-man “war of attrition” against the prison system from the imposing walls of Barlinnie.

“Barlinnie Prison destroyed me, but it also made me a better person,” Boyle, now 80, told the documentary.

“Every cell they put me in split up, broke down and got punished again.

“When I continued to rebel, they put me in what was called a silent cell. They came in and hit me.”

Even a transfer to solitary confinement was not enough to halt his campaign of disorder.

“All you have is a plastic pot,” he recalled.

“So I did what you do in the pot and I covered myself and when they opened the door I just ran at them. The three of them just slammed the door.

“Every time I went to the toilet, I steeled myself a little. There was a war of attrition. They didn’t know I was fearless.”

Such was Boyle’s impact on the prison system that it was decided in the early 1970s that he could not be restrained by normal means.

Instead, he was moved to the infamous ‘cages’ of the former Porterfield Prison in Inverness, where the only facility was a concrete block for him to sleep on.

He was stripped naked and given a blanket as his only possession.

On the wall was a list of rules stating that no prisoner should have been in jail for more than six months.

Boyle was there for four and a half years.

On one occasion he says he persuaded a corrupt officer to hide knives so he could pass them to other prisoners in the bathroom.

During the subsequent attack he was knocked unconscious.

He was taken to hospital, where a doctor advised officers to keep him inside overnight because he feared for his life.

The guards were unrelenting and returned Boyle to the cage.

He woke up ‘covered in blood’ with almost fifty stitches in his head.

But Boyle’s life changed in Barlinnie with the introduction of the “special unit”.

Through a green door, some of the country’s most violent offenders were held in conditions far removed from those of prisoners on the other side.

Shielded from view, staff and prisoners mingled in a more relaxed environment.

Cells had beds, television sets and more modern conveniences. Prisoners could even wear their own clothes and have pets such as cats, guinea pigs and rabbits.

It also included expressive activities, including sculpting under the gaze of pioneering art therapist Joyce Laing.

“Art was so far removed from our world. It was for the toffs,” Boyle said.

“She (Joyce) brought these seven pounds of clay. I made this portrait and it was like a dam broke. It was the first positive thing I ever did in my life.”

Boyle’s work, featuring sculptures of chained fists and the scales of justice, quickly attracted attention gallery owner Richard Demarco.

He offered Boyle an exhibition space at the Edinburgh International Festival in 1974.

To public outrage, Boyle was allowed to attend the show.

“I thought he should be seen as an artist,” Mr. Demarco told the program.

“I was accused of disgracing the meaning of art.”

By the time Boyle was released in 1980, he had also become a bestselling author– but the Special Forces controversy was beginning to irritate elements of the Scottish public.

Press releases from alcohol and drug fueled parties failed to quell the unrest and the unit was eventually closed in 1994.

In its 21 years in operation, a total of 36 of Scotland’s most violent and difficult offenders have passed through the green door.

Of these, only four reoffended. One prisoner took his own life and another overdosed on drugs.

No personnel were ever injured during the unit’s lifetime.

Boyle later established youth programs and programs to prevent those released from prison from recidivating.

“There’s no way I would be here if the Special Forces hadn’t existed,” he said.

“I have contributed to society. Do you want people like me to get out of prison the way I got out? Or do you want someone to come out and attack someone?

Modern Barlinnie is a world away from the violence-ridden ‘great hoose’ of Boyle’s day.

Since it opened in Riddrie in 1882, its five blocks have been overcrowded, with prisoners living in small spaces.

It was not until 2004 that each cell had its own toilet. Until then, prisoners still had to ‘throw out’ their own buckets into a communal toilet.

Such draconian conditions, combined with prisoners often held on opposite sides of warring factions outside the walls, earned it an ominous and violent reputation.

The promise that misbehaving children would ‘end up in Barlinnie’ has been an essential tool for parents for generations.

As one former prisoner put it: “Barlinnie is a bit like Guantanamo Bay in Glasgow”.

Contemporary prisoners can take classes to increase their education level, while a family center gives prisoners access to their young children in a more relaxed environment.

Levels of violence, while it is still a problemhave been greatly reduced from Boyle’s time.

But for Governor Mick Stoney, new challenges await.

About 80% of prisoners arriving at Barlinnie have problems with alcohol or drugs.

Mr Stoney describes a “constant and ongoing struggle” with illegal substances enter the prison.

The documentary shows officers searching a prisoner’s cell after a drone was caught delivering a package into an open window at night.

Mr Stoney said it was “inevitable” that drugs would find their way into prisoners.

Inmate Jamie, who was sent back to prison for breaching the terms of an ankle monitor, became addicted to drugs during his first five-year sentence for assault and theft.

He had been clean for five months before he relapsed.

He told the program that coming back to prison was “like taking someone out of rehab and putting them in a drug den.”

“I know it’s out there, I have to go look for it. “I don’t need that here,” he said.

‘He’ll come looking for me. And it will come to me when I am in my darkest moments.”

Barlinnie does will be replaced by a new prison, HMP Glasgow, on the site of the former Provan Gas Works.

No date has yet been set for its closure.

Mr Stoney said it was an opportunity to build a new legacy for the prison.

“Everyone wants a pound of flesh,” he said.

“There is a retributive approach to punishment, but restriction of freedom is a punishment.

“I want to replace the fame and notoriety of Barlinnie with a positive image for Glasgow. That this prison can make a difference for people, a real difference.”

Episode one of Within Barlinnie airs on BBC Scotland at 10pm on October 8. All episodes will be available on BBC iPlayer from October 8.