Talk about a tough audience. The crowd of prisoners gathered in the chapel of the Bar L to hear a trio of Scottish stand-ups might not, you would suppose, have a lot to laugh about.

But authorities at HM Barlinnie in Glasgow, Scotland's biggest jail, believe the prison's floating population of around 1500 inmates are in more need of humour than most.

They have drafted in three of the better-known names on the Scottish comedy circuit - Stu Who?, Scott Agnew and Alan Anderson - in the hope that it will help address some of the mental health problems among inmates.

David Gilmore, a PE teacher at Barlinnie who helped arrange the comedy event, said it was organised on the basis that "laughter is the best cure" for mental health problems.

He said: "Out in the community, something like one in four people will suffer from a mental health problem. In here, it is around 50%.

"Men being men, the people in here are likely to bury their head in the sand when it comes to dealing with these issues. If you talk about mental health initiatives it just turns people off."

As it turns out, prison comedy gigs are not a complete novelty. Anderson performed a Christmas gig at Shotts Prison, while Stu Who? recalls a string of shows held at prisons throughout Scotland in the early 1990s. "I did a load of gigs around then - Perth, Greenock, Aberdeen, Barlinnie. It was just after Jimmy Boyle had become famous for doing his sculpting inside and suddenly everybody wanted culture in prisons; art, sculpture, gigs, comedy..." he said.

For Agnew, though, the gig, was a "whole new experience".

Before performing, he said: "I haven't got a bloody clue how it will go. They could be absolutely fine; they might just be glad to see anybody".

Some 86 inmates eventually filed in to the Victorian-era chapel, clad in prison-issue orange jumpers and looking as far removed from a typical comedy audience as you could imagine.

All three comedians admitted to a touch of nerves. "They're usually very reticent to laugh," Stu said of prison audiences. "They're not in a very good mood - wouldn't you be? They don't know if they're there to be lectured. Some of them are quite hard men who don't want to be seen letting their guard down."

The biggest difference with prisoners, Anderson added, is that they're sober. "The guys are all up for it. They're a bit more reserved at first but, as soon as you get things going, they're a lot more responsive."

They needn't have worried. Within moments of putting on their mics, the comics were given a response that would have put Johnny Cash's performance in San Quentin to shame.

Anderson, who compered the evening, appeared to make friends early on by picking on an assortment of "fat b******s" and other random recipients of his gratuitous insults.

The rest of the content was, perhaps unsurprisingly, filthy. But there were surprises too. Agnew, an imposing, 6'5" figure, confessed, early on, that he was homosexual and braved the threat of any taunts by discussing his sexual activities in great detail. Crucially though, he still got the laughs.

Stu, who has always worn his working-class politics on his sleeve, said he is convinced of the appropriateness to performing inside.

"Comedy is about social comment and observation - who better to make it to?" he said.

"I've had people come up to me after shows and say that made me think', so it can have an effect."

David Abernethy, Barlinnie's deputy governor, concurred with that view. "By no stretch of the imagination could you say that Barlinnie is a nice place," he admitted, stressing that the comedy gig was one of many ways to help address mental health concerns within the prison.

"It hopefully will allow us to engage with people in a different way, by having a laugh. It's a way of presenting things that people wouldn't otherwise feel comfortable talking to us about."

So does the medicine work? With statistics released this week showing that 62% of Scotland's prisoners will reoffend within two years of release, no-one at Barlinnie was pretending that comedy would provide a magical solution.

Stu Who?, at least, appeared relatively philosophical about his impact. "I think if the show is bad enough, people won't want to come back. Maybe we can put them off jail that way," he said.