The truth means a lot to Tommy Tiernan. Yet he plies his trade in an area of showbusiness where the dividing line between what you’re seeing and hearing and the reality behind it is often blurry. Is that stand-up simply showing us a manipulated version of their real personality? Do they really mean what they just said, or is a point about something else being made? Are they simply playing a ‘character’, a constructed tool to offload some inner anxiety or bugbear? For Tiernan, a comic should be allowed to say pretty much what they damn well like, as long as the room and the wider context is right. And, most crucially of all, there has to be a truth underpinning it.

For the best part of two hours, we sit in a plush lounge of a central London hotel, Tiernan spilling his beans about the art and mechanics of stand-up, what fame means to him and the repercussions of some of the statements he’s made on stage. A sign just behind him on the door of the adjoining room catches my eye: The Honesty Bar. ‘One thing that keeps inspiring me is the notion of the clown,’ he says. ‘A clown show is full of real humility; he walks on defeated and that’s where the magic starts. If you come on stage, all cock o’ the walk, you’ve so much to lose. The constant thing of stand-up is, “how do I approach this? How do I give the best show, in terms of being a human being? How do I remove this ego stuff and how do I get more honest?” Because all the purest laughter between a performer and an audience comes from an open, vulnerable honesty.’ A pause, then a grin. ‘And if you can fake that, then great.’

Tiernan recalls going to see Slava’s Snowshow in New York a few years back and can still conjur up how wonderful he felt walking out at the end, knowing that he’d just had a real human experience. He made a promise to himself that he would work on that in his own act. ‘It can be just as thrilling going to see a comic who’s a bit more ‘fuck the world!’ as long it comes from an honest place; with Jerry Sadowitz, you feel that you’ve had a genuine human encounter. It’s about having an experience with an audience where you’ve gone to another place.’

An experience which took Tiernan to a very different place occurred last September during a wide-ranging interview in front of a live audience at the Electric Picnic festival in Ireland. Much knockabout fun was being had when he took a final question from the floor about whether he had ever been accused of anti-Semitism. Then began a long story which culminated in him being confronted by a Jewish couple who clearly weren’t fans. Through a construct of someone who was plainly, outlandishly hateful, he envisioned a scenario where he suggested that the Final Solution might not have gone far enough.

Simply to lift his exact words out of a much lengthier discussion about the limits of comedic taste and responsibility and you have an unreconstructed Nazi, a Holocaust denier and a subscriber to the BNP’s monthly newsletter, all rolled into one. Tommy Tiernan is none of those things. In simply showing up how disgusting some people can be, he has been misrepresented as a person with hate in his heart.

‘Once it had turned into a story, it became impossible to defend because you can’t stand behind words like that. There wasn’t a joke in there, just a stupid comment that worked then and there in that room, because everyone there knew what was happening. If I said something like that and meant it, people would be wondering what they were in the presence of.’

Within weeks, the story had escalated and little Tommy Tiernan from the tiny village of Navan had made the front page of The Jerusalem Post. His scheduled appearances on north American tours were cancelled and a few Irish comedians refused to talk to him (though plenty London-based Jewish stand-ups were very supportive). While he describes the incident as ‘kind of last year’, it clearly still rankles and he did address the issue during his two London dates in June; he’s not sure whether he will still wish to tackle it in August.

‘There’s a business connected to anything controversial, so when the Jewish thing happened it was an easy story, an obvious story. It was like following Shane MacGowan around and taking photographs of him doing heroin. Having said all that, it was a big moment for me, because I sat back and took a look at the type of comedy I was doing. I started to want to trust gentleness again, but without losing my balls or becoming impotent or television-friendly. When people come to see the show, I hope they don’t get a sense of someone being neutered. But the angry edge seems to be fading a little bit and the show is a little bit more playful now.’

Of course, it’s not the first occasion his material has resulted in a wave of condemnation, albeit often followed by less headline-making comments by those who were seemingly outraged. Tiernan once performed a routine about young adults with Down Syndrome and their very high sex drives, based on conversations he had with some of them and their carers. Once a couple of newspapers and a radio station had whipped up enough of a storm, Tiernan invited Down Syndrome Ireland to see his set and, surprise surprise, their leader saw no cause for concern, even making a statement to that effect for the media organs who had mischievously reported the original story.

It’s actually something of a surprise that Tiernan is willing to give up his time to members of the press pack given their role in enflaming such coverage. There was also the time he made a passing reference to the McCanns in a bit about putting your kids to bed (Tiernan has five of them from two different relationships): ‘three or four words, it took about seven seconds; was slightly mischievous, slightly cheeky. If you’d been to the show it wouldn’t have struck you as worth remarking upon. A journalist phoned the McCanns to see if they thought it was appropriate and the next day it was front page on a Sunday tabloid.’

He’s also performed routines about fundamental christianity and suicide rates in rural Ireland which have not made him flavour of the month with the morally indignant. For Tiernan, it always comes down to the context. ‘There have to be places where people can be mentally unstable in public. I’m not doing this stuff on Question Time or on Richard and Judy; it’s in a place where normal rules and behaviour are certainly not ignored, but the emphasis is on irresponsibility and wildness and funniness. That has to be protected.’

Tommy Tiernan has been wild and irresponsible and funny around these parts ever since his Edinburgh debut proper in 1997, sharing an hour-slot with Jason Byrne, before returning a year later with his first full solo show, reeling in a string of rave reviews and quickly filling out his Pleasance venue. While there was little doubt that he would walk away with the Perrier Best Newcomer in’98, he was elevated onto the shortlist for the main award, sharing space with Ed Byrne, Peter Kay and Al Murray. The List had a critic on the Perrier panel that year and when it was suggested that one of the other comics might actually win the award, he was quoted as saying, ‘over my dead body’. Such a statement could have been read as a slight on the comic in question, but was really more an indication of the strength of feeling towards Tiernan being crowned. And so it came to pass.

Soon after, the inevitable TV and film work came his way. He was cast alongside Omid Djalili in the not-terrible Channel 4 sitcom, Small Potatoes, was the host of the BBC’s Saturday night comedy showcase, The Stand-Up Show, and filmed a Comedy Lab for Channel 4 which included some of his Perrier-winning material. There were roles in films, too, in romantic comedy About Adam, and road movie Hold Back the Night. But there was something about all this post-Perrier activity that didn’t quite fit with the Tiernan mindset. ‘I’m not entirely sure what happened for a bit there, but I don’t think it was organic. You can be fast-tracked to over-exposure; it was an interesting experience but I’m very glad it’s over. There’s a very organic heartbeat in stand-up, a great beauty to it. It’s a shared tactile human experience. With television, if you can find the right shows then you can flower in them, but I never found one that I enjoyed doing for the sake of it.’

Many other comics with awards on their mantelpiece (Tiernan also won the So You Think You’re Funny award at the 1996 Fringe), and TV contracts being wafted under their noses would have just taken the riches and the fame, but Tiernan stayed focused on the work he felt born to do. He had made in-roads into north America and Australia but it’s the massive popularity he enjoys in Ireland that seems to give him the strongest sense of his comedy worth.

In Galway, he runs a storytelling slam night called Loose Lips and earned his place in the Guinness World Records for performing a 36-hour and 15-minutes set there. ‘By the time I had been onstage for 33 hours, I was having my Daniel Day-Lewis moment and thinking my father was in the crowd, but people were turning up with energy and their drink and looking for the craic. Remember those bits in Lord of the Rings where Gollum was vulnerable? I was a bit like that.’

As Tiernan re-enters Edinburgh for ten shows called Crooked Man, it’s with a new sense of who he is and how he wants to be seen as a comedian and artist. ‘I’m really enjoying stand-up for the first time in a few years. I think you just go through phases of a particular type of energy. The stand-up in the past was a lot darker, was more about tension and being loudly curious. Miles Davis did this double album, Bitches Brew: I think I’ve had my Bitches Brew period. I’m going back now towards Kind of Blue.’

Tommy Tiernan, Gilded Balloon Teviot, Bristo Square, 0131 622 6552, 20–30 Aug (not 26), 8pm, £14–£15 (£12–£13).