They didn't take their lighters out, but they did sway. Unselfconsciously, like young fellows at their first pop concert, even the older ones who sat at the back.

They stood on their seats. They danced. They sang. They grinned and punched the air, wolf-whistling as Christy Dignam, the barefoot lead singer of Aslan, stripped to the waist.

A handful sat staring, smoking, not even tapping their chunky trainers in time to the beat. But they still sat where they had a view of Aslan, the band from Finglas, north Dublin. The rest of the room went mad.

It was Wednesday night in Wheatfield Prison in Clondalkin, west Dublin. And it was Aslan's second gig in the prison. "They'll be talking about this for weeks now," one prison officer said as he let the band and their crew out of the hall, where they had played for an hour and 15 minutes to about 150 inmates.

Take away the 18 or so uniformed prison officers who lined the walls of the hall and it would have looked like a school concert venue. The backdrop had been painted by an art teacher who works with the inmates, and the chairs were bolted in place in front of a large stage.

Dressed in T-shirts, sweatshirts, tracksuit pants and the regulation trainers, the inmates took their seats shortly after 5.30 p.m. They were almost all under 25.

Under the watchful eyes of prison officers they were less boisterous than your average stag party as they waited, distracted only by the reporter and the music company woman. "I'll give you something to write about," one youth shouted when he spotted the notebook.

The only other woman in the hall not wearing a prison uniform cowered in her seat and admitted to being more intimidated than she expected.

The band came on to a piercing wolf whistle and roars of approval. "G'wan, Christy," they shouted.

"We were doing a sound check and I think I dropped a 10-spot about five rows back," lead singer Christy Dignam said. "So if you find it can you give it one of the officers to give it back to me?" The joke, discussed minutes before backstage, had originally featured a £20 note.

Afterwards Dignam looked a bit sheepish about his colourful language and his Roddy Doyle-like references. He doesn't normally do that on stage, he said. But the more lewd he got the more they loved it.

But they also sat rapt, all eyes on the stage as the band performed Hurt Sometimes, a song described by Dignam as about "getting your heart broken".

Then a prisoner in a white sweatshirt stood on his seat and danced. A prison officer's torch picked him out, throwing his shadow on the opposite wall. He kept dancing. The torch snapped off. Soon most of the prisoners were doing the same.

A crew-cut prisoner in an Adidas top turned towards the audience and clapped his arms over his head like a groupie as they sang along to Crazy World.

Then the white sweatshirt got his moment as he shared a microphone with Dignam, telling the singer they had the same surname. Thin and grey-faced, the prisoner looked about 16, but officers said afterwards he was in his 20s. "When Oasis start doing Aslan songs I'll start doing Oasis songs," Dignam shouted at them, after repeated requests for Wonderwall. But there was no holding back the tide. The white sweatshirt hauled himself on stage, took a swig of water like a real pro and did a solo rendition of Wonderwall, accompanied by most of his fellow prisoners singing in tune and in time.

He gave it his all and finished with both hands clutching the mike to his mouth. "Maaaybeee you're gonna be the one that saaaaves me." Then with a grin he hopped back down to join the audience.

"It's a captive audience," Dignam said, before he went on. But it was also a more responsive audience than most on the outside. "In prison the only kind of connection they have to the media is the radio so they listen more than most people."

So what about the taxi-driver who remarked, "Well, they have a grand life," when this reporter told him the reason for going to the prison?

"That's something I thought about," Dignam said. "If you take somebody's liberty away from them then that's the punishment. Whatever we do is going to have no relevance to their sentence."

And what about the victims of these youths, described by one officer as the ODCs, ordinary decent criminals - muggers and robbers.

"I'm probably a victim," Dignam said. "My house has been robbed and my car. And it could be someone in the audience who did it. But it's the time of the year to be a bit charitable."

For some even the idea of a pop concert in a prison conjures up images of wet liberals getting misty-eyed over the rights of thugs and muggers.

But for the prison officers the annual concert is like releasing a pressure valve. The majority of the young inmates of Wheatfield are transfer prisoners, finishing their sentences.

The State's first purpose-built prison, it was opened in 1989 as a juvenile facility. Now about a third of the prisoners are sex offenders, classed as protection prisoners, as they are separated from others after one inmate was attacked. None of the protection prisoners was at the concert.

Last July a 25-year-old man hanged himself from the bunk bed in his cell, using a pair of shoelaces. He was serving a sentence for a number of robberies, including acting as an accomplice in a robbery in which a taxi-driver was stabbed with a syringe.

Wednesday's concert was rounded off with a second rendition of Crazy World, and then the Beatles' Hey Jude and it was all over. The lights came on. The band went off and the audience turned to look at the onlookers. A wall of faces grinned, leered, shouted and wolf-whistled.

They lined up along the left side of the hall and were separated into groups of about 30. Within minutes the hall was clear, with only a few cigarette butts left on the floor. They were going back to their recreation rooms. They would spend about 20 minutes there and then be locked into their cells for another night.