TOMMY Tiernan represents serious intrigue. How can you not be drawn to a man who once considered becoming a missionary, yet has gone on to create huge laughs with the coruscation of others’ ideals? How can you not appreciate his recent deliciously dry performance in Channel Four’s Derry Girls?

And what to make of his outrageousness, when he declares, for example, that “Junkies should be given as much heroin as they want and be made to live as pets for old people.” Or when he suggests we should leave old people to die, as nomadic tribes once did.

Where does this come from? Is the business of dark, provocative comedy borne out of existentialist angst, his life punctuated by periods in Jungian therapy? What a life, so far, you suggest, as he relaxes in a Dublin hotel during his current tour. “Not really,” he says, deadpan. “I’m like the Wizard of Oz. There are lots of bells and whistles but a very small man beneath it all.”

Mmm. Let’s talk about the bells and whistles. Tell me about the impact of being part of a family that moved around a lot, Tommy; born in Donegal, the family moved to Zambia, and then on to London and back to Ireland. First up, was Witness Protection involved? “I wish it were something as exotic as that,” he says, grinning. “In fact, it was my father who believed that peace could be found in other places.” Well, at least he took the family with him? “Yes, that’s true. And he had a job to go to, working in agriculture. We came from a long history of teachers, and my father’s job was basically talking to farmers, whether in Africa or whatever.”

Tiernan’s comedy features heavily on self-deprecation and self-analysis. Did the nomadic nature of his early life – continually leaving friends behind – cause him to look inside his head all too often? “It’s very hard to diagnose yourself but it’s fair to say it certainly gives you a sense of wanting to belong to a group while being outside of it.” He adds, grinning; “An amateur personality profiler could easily see the link between someone going up there on a stage and trying to ingratiate themselves into the affections of a crowd.” He adds: “It’s hard to diagnose a stand-up. But I definitely have a memory of being a new boy in class, lots of times, and one day you look around and all your classmates are brown.”

The teenage Tommy, now back in Ireland, living in County Meath, found it hard to fit in with the world. As if his sense of displacement weren’t difficult enough to rationalise, he was sent away to a religious boarding school in Galway on the West Coast. Does he blame his parents? “I think we’re all making it up as we go along. And in the heat of the moment you make decisions. You don’t see the full context. As someone who struggled hugely with school life, I had failed all my exams and my parents thought ‘This kids needs a different environment.’ So I arrived home from school one day and they announced; ‘Look, we’re going to give you a new start and I was sent to the West coast.” The teenager was in fact happy to go. “Yes, and it began a love affair with the West which I’m still in awe of.”

He wasn’t in love with himself however. Tiernan was a poster boy for teenage angst. He developed a fixation with a female, sought out a social worker counsellor and at one point the principal only allowed him back into school on the basis he wouldn’t talk to other students about religion or politics. “I look back and realise how naïve my controllers were,” he says with a wry smile. “They imagined a box that doesn’t exist.” They should have noticed a young man searching, desperate to improve life. At school he tried to set up a St Vincent de Paul Society. He visited long-term psychiatric patients in hospital.

On leaving education, Tiernan was determined to save the world, or at least a part of it, and set to join the Redemptorists, the Catholic missionaries. The turning point came when another seminarian declared a special devotion towards Our Lady. Tiernan felt his special devotion was towards Belinda Carlisle. “I realised there and then I was in the wrong hotel and had to leave.”

Tiernan didn’t hook up with the rock singer but found love with a girl he’d met at a Christian retreat, and they went on to have three children together. Before the first child was born he had turned to stand-up, but then birth of the baby produced a realisation he had better provide, and so he focused on a career. Tiernan’s big break came about in 1994 when he won the So You Think You're Funny award at the Edinburgh Festival.

Had he felt he was funny before this point? “I have absolute memories of seeing the classroom as my first stage, but along with a lot of other comics, I wouldn’t have been the funniest guy in the class. I would have consistently qualified for the Champions League. But I would never have won the championship. I was the Arsenal of wit in my class.” He adds: “The guy who is third or fourth funniest always works out how the first funniest guy works.”

How does Tommy Tiernan work? His act features a study of how we get by with our ordinary lives, asking questions about relationship longevity, sexual interest, always layered with provocation. He once declared: “In nomadic societies, if an old person couldn’t keep up with the tribe they were just left to the wolves. And now that we’ve lost our nomadic lifestyle it doesn’t mean we should lose that principle.”

He admits he loves to play with tension. “It’s the Geiger counter you have at that moment and the audience’s inability to live with that tension. So you diffuse the tension by introducing something stupid that makes people laugh. There’s a contract between the audience and the comedian. You can talk about anything, offer a message or an absurdity. Or you can be like Frankie Boyle and have an agenda of outrage. And the audience will accept any of this as long as its funny."

Does the effort of creating comedy hurt? “I don’t equate it to going into a hot kitchen and cooking for eight hours or being a nurse. If you can accept the ordinariness of the labour of it, it’s just work.”

Yet, getting up on stage is so much more seductive and affecting. He gets rapturous applause. Therefore, the pressures to sustain this must rise exponentially? “Yes, that’s true. But you can separate what I do into two areas; the work in coming up with the show is ordinary. You’re in a room with a piece of paper. Yet, the other end of it is an adrenalin-based life. When I was growing up I was mad for sport – I was playing soccer all the time – and I think stand-up, the intensity and the physical experience of it all has replaced that for me.”

Does he feel he is communing, if we can use that word, with an audience? “Yes, and I don’t think we should be afraid of words like ‘communing’ because that’s what we seek, absolutely. It’s a bit like when I take my kids to watch Liverpool play; there’s a sense of common purpose and you can get that in theatre shows as well.”

Women have long intrigued and captivated Tiernan – he split from the mother of his three children and now has three more with his wife – and they have provided on-stage material. “There’s a line I’ve been using in my stand-up recently in which I say ‘I’m mad for women. I love female company. I’m crazy for their approval, their kindness.’ But if I stood up there on stage and said I worshipped them I’d be worthless as a comedian. You have to test boundaries. So I address women specifically – it’s about slagging them, but not in a mean way, more in a refusal to take things seriously. You see, the stage isn’t a place for respect. It’s not the place to take anything seriously. But your disrespect can’t be toxic.”

He expands, grinning: “If you are standing on the San Andreas Fault Line and you’re in a room with a guy who is running around shifting the tables you want to tell him to stop and behave. Given the debate on gender politics at the moment, to have an idiot in the room who is knocking lampshades over while the room is shaking is not helping. But part of the experience of being on stage is to shake things up.”

He’s a deliberate subversive. Yet, at the same time, he can’t help himself. But is this dangerous? We live in a time when people love to be annoyed. How does he feel about the reaction to his comedy when, for example, he tells husbands and wives the two greatest words they can can utter to one another are ‘You’ll Do’. “As you get older you become a little kinder,” he says, smiling. “I would never want an individual to feel uncomfortable. But at the same time there has to be an air of generous recklessness about your performance,” he adds, laughing. “And if there is a chorus ready to be offended then f*** dem.”

He’s still the schoolboy who asked so many questions of others. Now, he creates and releases tension for a living. “I talk about abortion or refugees or the health service, but you have to get a laugh out of what you’ve just said. It’s an odd collaboration. If you’re too unhinged people won’t relax. And if you’re too safe they won’t laugh. You have to go on instinct.”

He quotes the classic Spike Milligan line, who when being presented with an award was told of a special message from Prince Charles. Milligan cut in with “Grovelling little bastard". Tiernan loves to be a bit Spike, to have a 48-year-old voice that’s still being valued by the crowd. “A few years ago I did a gig with Rich Hall – and whatever age Rich is he looks older. But I remember feeling reassured and delighted that Rich looked like he didn’t look out of place on stage. I find that so encouraging that voices of actors or writers or musicians are valued more as they get older. Comedy is not just a young person’s game. It’s not like being in a boy band and you hit 31 and you think ‘This is a bit perverse now'.”

Tiernan will finish this current tour and immediately begin another. He works constantly. It suggests he needs to be up there on stage. “This is probably a shameful thing to say but this (comedy) still feels the point of my life. It revitalises me.” Does it make him happy? “No, I wouldn’t say I’m happy at all,” he says, laughing. “But I’m not unhappy about it. We all suffer, but like most people my suffering is tolerable. Each day has enough peaks to get you through the trough.”

Is he tolerable to others, given his quixotic mind and moods? “I know my wife finds me very difficult to live with,” he says, with a knowing grin. “And so do my children. But I find them difficult to live with too. At least we have the honesty to admit that to one another.”

A recent break-off in his working life was the appearance on Channel Four’s Derry Girls, in which he gave a lovely performance of the whipped, beaten father. Tiernan was in his natural element. “It was fantastic,” he says. “I think the writing by Lisa McGee is wild and chaotic. I love the boldest scene in which the dog pisses down through the roof and the piss runs down the face of the statue of the Virgin Mary. That’s the wildest thing I’ve ever seen. (Meantime, there’s a dead nun lying on a desk.) Is shows you can be anarchic if you’re coming from a place of fun. If it were Dom Jolly pissing on the Virgin Mary you have to question if you’d be laughing.”

Tiernan’s popularity suggests he has the balance of assault and shock comedy just about right. He sells almost as many DVDs as U2. We know when he goes too far he probably knows he’s gone too far. But there’s little doubt the world has benefitted from this clever mind that’s always searching – and seeking approval.

You point out, smiling, that it’s interesting Tiernan has gone from a child who moved around a lot to an adult who’s constantly sleeping in strange beds. “Yes, I’m still the new boy in school and I replicate this every night in a new town,” he agrees. “Along the way, I’ve picked up the ability to talk to strangers.” He adds, in soft voice, smiling: “We all find ways of fitting in. Not belonging is my way of fitting in.”

Tommy Tiernan, Under The Influence, The King’s Theatre, Glasgow, March 14