Ciaran Carson is looking very much the dapper elder statesman of letters these days, at least for a reading from his latest book, Shamrock Tea, at Belfast's annual literary festival, Between The Lines.

Like Fishing for Amber, his last work, the new book is a swirling kaleidoscope of stories of which the central focus is the celebrated Arnolfini portrait by the Flemish painter, Jan van Eyck. Did Carson employ the same working method as with Amber, and in particular, was the "library angel", that guiding spirit of the literary hunter-gatherer, in evidence?

"Day by day, I was wondering where the story would go and what would happen next. One does sketch out a rough kind of plan, but you have to hope that each day you stumble on some kind of interesting notion or incident or some piece of historical nonsense, and that's the way it happened. I'd say it was a matter of serendipity, accident, and planning. But the library angel is still there, yes. He must be on a long-term contract with Belfast City Council."

To hear Carson talk, you'd think the book was a mere mishmash of fortuitous incident and coherence, with, as the book's blurb says, only "meandering connections" between the stories. Instead it actually reads as though constructed with almost mathematical precision.

"That's just the way it worked out. How much is planned and how much is worked over in retrospect I really can't say. It's the old matter of saying: Once upon a time there was a King in Ireland, what did he do, what did he wear, what happened to him . . . you invent the story as you go along. I don't know if you can say there's such a thing as a plot in the book, but I think there is at least a definite sense that one thing leads to another."

Perhaps then there's as much plot to the book as there is to a football or hurling match, and Carson has compared writing to playing sport: a matter of style, technique. But if it's a valid comparison, isn't there a danger of substance being relegated to the bottom division?

"It's like sport in the sense that you have to put in all those boring hours of practice, you know, knocking a ball off the wall day after day, week after week, month after month. Then, during a game, you score a wonderful and apparently spontaneous goal. But is it purely spontaneous? There were all those hours of practice, having the idea of the thing always in mind, wondering what it might be like. So it's that kind of line between imagination and fact. "Style is about the thing itself, it's not something stuck on to the matter or the substance. I think there's an illusion going round, a fallacy, that the poet, if he writes a poem, has an idea and then he sticks the `style' stuff on it, makes it rhyme or scan, whatever, puts the idea into a certain form." Has the new book taken him away from his original calling? Is he still writing poetry?

"I haven't actually written a poem of my own for some time, and I'm beginning to wonder if I still can, although that's a fear - or a slight anxiety - which hangs over you all the time, whether you're a poet or a prose-writer. The main thing at the moment is that I'm working eight hours a day on a version of Dante's Inferno, in terza rima, [the original, and notoriously difficult, three-line verse form of The Divine Comedy] it's been tough going the last four months. A full-time day-job in fact. "

What do you do for a day-job Ciaran?"I'm down in the Inferno hacking away at the coalface!"

Whether producing original poems of his own or not, Carson's view of poetry hasn't changed, seeing it as just one particular language of expression among many others, and relating it to the basic philosophical question of how one views the world.

"All the things of the world are like each other in some way, and the world is one thing in some sense while at the same time being a multiplicity of different things. It's up to yourself, at the end of the day, whether you agree with Wittgenstein that the world is everything that is the case, or whether the world is everything that is the case plus a lot of other stuff as well as that - which it might well be. "There are many ways around things. I know for sure that what you say in French is not the same as what you say in English, if there are ideas behind what we say they're not the same in Irish or in Hindustani or whatever. To imagine that something can be said in only one form or language is a mistake, I think. Mind you, once it's said in one way it only speaks that one particular thing."

Shamrock Tea would certainly translate well to the cinema screen, with its spiral sequences of colourful vignettes, flashbacks and dramatically charged scenes. Perhaps Carson would consider following Roddy Doyle's example?

"I would like to, but I haven't been asked. If there's anybody out there who wants to give me a lot of money to come up with a script, I'd jump at it - the script I mean."

For all its time-hopping and trans-dimensional scope, the book does create the sense of a very closed, self-referential, split world. This impression is hardly a surprise to Carson. "It's about madness at the end of the day. You could say that the whole book is about somebody who's actually insane. He's even in hell maybe."

One aspect of this hell is undoubtedly the perennial Carson obsession with exile. Does the writing exorcise this particular demon, or does the author remain as fugitive and fragmented as the narrator of his book?

"When it's going well you do feel that you enter into another world, as if you're exploring that other world, it's quite uncanny. And the knowledge that, whatever you write, it's true, because it's the real world, is also uncanny. But at the end of the writing you're not sure which is the real world: the one you've written or the one you physically inhabit. The world in Shamrock Tea is a curious, interesting world - I hope - but it's not all pleasant, there's a definite dark side to it."

Darkness there is, present to the same degree as in van Eycks's Arnolfini portrait. But it is also a multi-faceted world reflecting the order, beauty and mystery of our own. One of the book's strengths is that it reminds us of some of those deceptively simple philosophical ideas that everyday life makes us forget. "All of life is a great chain," says Uncle Celestine, "the nature of which is known when we are shown a single link of it."

Shamrock Tea is published by Granta, £14.99 in the UK.