"So I'm sorry to disappoint, but I'm a fairly well-adjusted human being," he says in a gentle Irish lilt that makes melodies of sentences. "And I'm not particularly prone to depression, either. People tend to think that this is inevitably the case with comics, but I don't think it is ever actually true. Name me one comic who has ever suffered from depression."
Off the top of my head, I tell him Tony Hancock. "OK," he concedes, palms up in defeat, "I'll give you that one. There's always the exception that proves the rule. Another?"
I give him Spike Milligan, John Cleese, Peter Sellers. Even Victoria Wood, I say, has battled her demons. O'Briain is frowning now, and so I offer him one more: John Belushi. Poor guy drank himself to death.
"John Belushi? He wasn't depressed! He was just a happy drunk, although it's probably true to say that he drank a little too much. But, OK, fair enough, I take your point, you smug bastard! Though I'd still say depression in comedians isn't on an epidemic level, it's just that comedy, by its very definition, must rely on a certain level of misery in order to work. It's what makes you funny. You can't, for example, do a routine about being a new father taking joy in your new baby. Do that, and you'd lose the room immediately; the energy would just evaporate. I know about these things," he adds, expertly. "I've read about them in books."
He tells me about one particular book he much admires. It's called Laughter, by an American neuroscientist called Dr Robert Provine, apparently the world's leading scientific expert on laughter. In his book, O'Briain says, Provine investigates aspects of its evolution, its role in social relationships, its contagiousness and even its health benefits.
"It's fascinating stuff, it really is. Provine walks you through the very mechanics of laughter, and so for a comedian, it's an essential How To book. Did you know that in the comfort of your own home, you will rarely laugh out loud, no matter how funny you happen to find something? But if you were in a café, chatting among friends, you'd be far more likely to laugh a lot. Provine learnt that only a third of the time do people laugh at jokes. Most of the time, it's simply a nervous mechanism, a breaking of tension. Audience members laugh at comedians because other members of the audience are laughing too. It's a social thing. And so, as a stand-up, all I do is break their collective tension. I lift the audience up and drop them, I push and push them until they fall."
It's probably safe to assume, I say, that Jim Davidson doesn't approach his comedy quite f so theoretically. "Probably not, no," he says, now breaking his own tension with laughter. "But then, that's me, I'm afraid - a complete and utter geek. I'm not particularly proud of the fact but, hey, what can you do?"
When he first began popping up on British TV screens a few years back, Dara O'Briain was already a household name in his native Ireland. But this, he now suggests, wasn't much of an achievement. Irish TV is a very small pond; anyone can dominate it if, he says, "you manage to do a few different kinds of programmes over there, which I did. After that, doors started opening up, in all directions."
His big British breakthrough came courtesy of a post-Angus Deayton series of Have I Got News For You?, which he hosted with the aplomb of someone who has been hosting clever-clever panel shows for much of his life. He proved an instant success and was invited back several times, despite occasionally landing himself in hot water. On one show, an offhand comment of his about Elton John's role in the stage production of Billy Elliot provoked criticism from a gay-rights group, who said they would complain to the BBC about his "offensive and cheap" remark. The BBC defended him saying the line came from a team of writers, and the uncomfortable brouhaha fizzled out - except on the internet, of course, where it continues to incense those who incense easily.
The comic's evident ease as TV host then paved the way for more of the same, and suddenly he was everywhere. Here he was, this apparently middle-aged Irish fella, finding himself a bonafide Next Big Thing when most bonafide Next Big Things still have all their own hair and the kind of bottomless blue eyes women yearn to dive into.
"Yes, hmm," he glowers. "Middle-aged. I get that a lot, but I'm only 34, for fuck's sake! But then, I've had that all my life; I'm used to it. I've always looked older than I am, like everybody's dad. When I was nine, I looked 11, and so on. I've never been ID'd in bars - never. Once, I based an entire show on me looking older than I was. I asked the audience to guess my age: the average turned out to be 37." The pause is a painful one. "I was 29 at the time."
But O'Briain, a man who applies scientific logic to much in his life, has come to see the positive side of it.
"The game of comedy is all about owning the stage," he says, "and from a physical point of view, it's beneficial that I'm a larger man. From my lumbering presence alone, I can't really help but dominate the stage."
But his success here relies on far more than just presence alone: he has a most mellifluous way with words, too, an incessant gentle patter that somehow elevates what is essentially a fairly traditional routine - he jokes about family members, students, a notional girlfriend - into the realms of the very funny. He says he's always loved words, adored English at school, but was drawn inexorably towards numbers.
"I was obsessed with maths," he says. "I was your prototype science geek, I'm afraid."
At University College London, he studied mathematical science. "To what end? I never even considered that. I just loved my numbers, sad as that makes me sound. But the trouble with maths at university level is that it was also the favourite subject of some insanely, savantly clever people, which doesn't exactly make for a fun social life. And then there was the fact that in our class there were just two people: me and Gavin, nobody else, for four years."
It was because of poor, pitiable Gavin that he sought a social life elsewhere, eventually enrolling in the debating society. Though his perfectly healthy upbringing had made him a perfectly balanced teenager, he nevertheless craved an audience. Folk in the debating society were popular, and O'Briain wanted popularity. Pretty soon, he got it. He began writing for the university newspaper as well, and later took it upon himself to host orientation meetings for freshers: "Yes, I was that prick, the one dressed in a tuxedo for no particular reason, looking like a right idiot." He shrugs his shoulders. "I couldn't help myself."
After graduation, he realised that his love of mathematics would find no place for him in the real world, and so he began working for a local Irish newspaper, The Sunday World, in which he wrote a weekly column entitled Get A Life: "700 words of whimsical nonsense." He was also dabbling in stand-up comedy, Provine's Laughter in his pocket, and for the next five years he hustled and gigged wherever possible, eventually landing a TV spot in Ireland, hosting a children's programme called Echo Island. From here, he hopscotched over to comedy-driven current affairs show The Panel, which, in time, would lead to HIGNFY and beyond.
"After that, everything came very quickly for me, and it surprises me still," he says. "I seem to be all over the place at the moment, and I find myself sitting next to the likes of Stephen Fry, Bill Bailey, Paul Merton - people I've worshipped for years - feeling like a tourist. But then that's probably a good thing. I mean, I wouldn't want to start taking it all for granted."
"Ireland's best-loved comic", as he is now so often hailed, is indeed "all over the place". He has appeared on Jonathan Ross's chat show, he has done Parkinson and Jack Dee. Last year, BBC2 gave him his own programme, Live Floor Show, "but it was stuck on at 11 o'clock on a Saturday night, and nobody watched it". He has hosted Mock the Week for the same channel, a programme not entirely dissimilar to HIGNFY, and is a regular guest on Stephen Fry's QI. He has done something for BBC3 called The Last Laughter ("A Fame Academy for comedy writers"), and even sailed down the River Thames alongside Griff Rhys Jones and Rory McGrath in a programme called Three Men in a Boat. He's currently recording a new chat show for BBC2, Turn Back Time, in which he extracts embarrassing memories from his guests - including Terry Jones and Barry Humphries - using archive footage and asks what they'd change if they could do it all again.
Clearly, then, the man will do anything, so long as it's on the telly. Correction: almost anything. "I once did a quiz show for [the Irish channel] RTE called It's A Family Affair, and it was disastrous," he says. "I won't be doing that again. TV feels comfortable for me and I'm happy to go along with most of whatever comes along. But I'm definitely happiest when I am on stage. It's certainly where I think I'm best."
To this end, he has just completed a lengthy tour of the UK, and is already working on ideas for his next stand-up show, which he intends to squeeze in whenever television permits.
O'Briain polishes off his orange juice with a final concerted suck on the straw, and checks his watch. It is now a little after midday, and he must dash. He has an appointment at home with a bookshelf that requires assembling. Later, he is meeting the girlfriend he refuses to discuss ("for private, enigmatic reasons") for dinner. As we leave the bar, we chat casually about music. It transpires that the 34-year-old who looks like a kindly Van Morrison buff is in fact a dance-music fan. He loves Chemical Brothers, LCD Soundsystem, Basement Jaxx. But he concedes, slightly sadly, that his clubbing days are long gone.
"I mean, look at me," he says, indicating the suit, the build, and the demeanour that reeks of old smoked maturity. "If I go to a club these days, I'd probably kill the atmosphere stone dead, wouldn't I?"
His smile produces crow's feet. It's a pained expression, full of pathos and hope against hope. I do my best to avoid telling him what he already knows.
'Turn Back Time' airs later this summer on BBC2Reuse content