In 1973 Barlinnie found a more humane way of dealing with Scotland's hard men by opening its controversial Special Unit.

For the first time prisoners were allowed to wear their own clothes, listen to music in their cells, and have open visiting.

Attempts were made to rehabilitate and humanise them through art, literature, and drama until the unit closed in 1994.

It's most famous and successful member was murderer turned sculptor and novelist Jimmy Boyle.

Boyle, who was jailed for life in 1967 for murdering William 'Babs' Rooney, had previously attacked prison officers and staged dirty protests at various jails across Scotland.

His subsequent rehabilitation – from violent gangster to cultured artist – aroused controversy at the time and he was never far from the headlines.

Boyle discovered a talent for sculpture and designed the largest concrete sculpture in Europe called “Gulliver” for the Craigmillar Festival Society in Edinburgh in 1976. 

Read the full series: Barlinnie - the story of Scotland's super prison

In 1977 he published his autobiography, A Sense of Freedom, while behind bars which was turned into a movie starring David Hayman as the killer turned artist.

It became a bestseller and told of his life of crime, murder conviction, and eventual rehabilitation in the Special Unit.

In 1980 while still in prison, he married public school educated psychiatrist Sara Trevelyan who had visited him in the Special Unit after reading his book.

Her father John Trevelyan was secretary of the British Board of Film Censors, a pillar of the British establishment.

Since his release in 1982 he has become a successful commercial artist and property developer and now lives in Morocco.

Sara remembers her first visit to Barlinnie prison more than 45 years ago as if it was yesterday.

Then Barlinnie had an X certificate rating in the prison system.

The Herald: Sara Trevelyan with Jimmy BoyleSara Trevelyan with Jimmy Boyle

Sara's subsequent relationship with Boyle became a media sensation at the time.

By her own admission she had had a fairly sheltered up bring and nothing would prepare her for the first sightings of its grim grey walls.

Sara is planning release a book later this year about the Special Unit which will mark 30 years since its closure.

She said it was quite a remarkable establishment and hopes the new jail will learn lessons from Barlinnie’s controversial experiment in rehabilitation.

Sara: "It was not without its issues.

"The unit was such a contrast to the rest of Barlinnie Prison.

Read more: Barlinnie: From beacon of prison reform to notorious superjail

"My first impression of Barlinnie was the fortress like facade and Victorian edifice.

"I remember going across the yard to a very small gate into the special unit with its paintings and artwork."

Sara added: "It was more like a hostel than a prison, which in many ways it was.

"The prisoners were allowed to wear their own clothes.

"The officers were really friendly and people were calling each other by their first names.

"There was art and murals inside the unit and prisoners decorated their cells individually and they were able to invite their families in.

"It was possible to visit seven days a week."

Sara first visited Barlinnie in 1978 after writing to Boyle, whose book she had read.

The Herald: Find every article in The Story of Barlinnie series here

He then sent her a visitors pass and they met for the first time. However it would be another year before they met again.

She added: "We began a friendship and I would visit more regularly.

"I was able to visit as I often as I liked which was not the case in the mainstream prison."

Her censor father was a great supporter of prison reform and she had previously visited Holloway women prison in London.

Sara was well aware of Barlinnie's reputation before her arrival.

She added:"It shows that they were thinking about prison in a different way to now where they are more like warehousing which is what it has become.

"I saw a different side to the prison as all my visits were to the special unit.

"It was a different approach to prison particularly in the use of the arts.

"It became an anomaly in the prison system."

Read more: Glasgow's forgotten prisons and why Barlinnie was built

Sara says that the new jail should draw on the lessons of the special unit.

She added: "Are we going to think about what brings people into the prison in the first place?

"Is there going to be support for people when they finish their sentences so that they make better choices?

"My hope would be that some of the spirit of the special unit would go into the thinking of the new prison.

"Particularly the relationship between prisoners and prison officers.

"It is not about building a new building but bringing in an attitude and approach that has hope at the core of it."

The Boyle's married in Balfron Registry Office in 1980 while Boyle was still in the special unit.

The couple went on to have two children after he was released from prison in November 1982 and are now divorced.