He's just published his fifth book in the phenomenally successful series, Artemis Fowl and the Opal Deception, which is another adventure through the fairy underworld with all manner of technological wizardry. But unlike a certain other children's author, Colfer likes his technology to have a basis in science. The latest plot involves an attempt to get to the centre of the earth, which was inspired by a scientific article.

What I like about it is it's possible, " says Colfer. I don't like books where you have a spray that makes you invisible. I like it to be scientifically almost possible."

Colfer's books are packed with fantastical devices, but like the science, all of them seem to be not-so-distant future versions of our current technology. Colfer says he makes a concerted effort to keep up with the technology that is second nature to his audience. It's just life to them. I remember when the first Artemis books came out, parents said to me, 'I really liked it but I think there's a bit too much technological stuff in it for the kids to understand' and the kids were like 'daddy, you don't understand it'. And that's true, a 12-year-old would be way ahead of me, but I do try to keep up to date. Every gadget that comes out, I buy it for the good of the literature, " he says, with a completely straight face, before breaking into a grin.

Colfer's watch looks like just such a gadget although he explains there's a more serious reason behind the large, smooth face with the giant digital numbers. ?I can't see anything out of this eye, " he says, so it's an old-man half-blind watch." The retina in his left eye slipped when he was hit by a car in Saudi Arabia. ?It was funny, " his says, which seems typical of his light-hearted approach, ?he [the driver] went past me, so I crossed the road, but then he backed up because he had missed his turn. I can see a bit now. They reattached the retina but you don't get the sight back sometimes."

Colfer, an ex-teacher, says he likes to make his books as challenging as possible for his young readers and says in that respect he is still very much a teacher. I remember one of the first books I wrote somebody said to me, there's an awful lot of hard words in this and I said, 'Good! If they don't know them they can look them up', " he says in his best outraged voice. You realise that's a real teacher's thing. I find myself watching art programmes and looking for lessons or if I see leaves I think I should pick those up now because they'll be good for printing. When you're a teacher you think like that all the time. I was doing a reading and there were some girls messing down the front and I found myself giving out to them, saying 'there's people trying to listen and you two are talking about your hair bands' and then I was thinking, 'this is not what I'm supposed to be doing'."

Colfer first got into books as a child himself, but unlike many teenage boys, he stuck with them throughout his adolescence. Boys just seem to lose interest in reading a lot, but then there's the small group that become absolutely fanatical and I was one of those and it had a lot to do with puberty and girls and football and just general testosterone. Boys just want to run around banging their heads against trees and shouting at girls, because girls like that. When I was a teenager I wanted to be doing that as well but I always held onto the reading."

Colfer says the gender divide of his audience is getting smaller; the current rate is something like 70% male, 30% female. I think about 20 or 30 years ago when I was a kid, things were deemed 'suitable'. So boys got all the action and girls got the ponies and the ballet and they had boarding school too. And now it's much more spread across. There's someone writing something for everyone so you can read about what you want. But there's still this thing that boys are given the action books and girls are given the pony books so you have to try and break out of that."

The big question is whether Colfer will break out of children's fiction and into writing for adults when the Artemis Fowl series is finished, (he says he only plans to write six books in the series, seven at most). The big people , " says Colfer, again mock-serious. I've just done a story for Ken Bruen's new anthology. Ehh. . ." he trails off, suddenly distracted. I just saw a pair of legs, " he said, ?all I saw was legs."

Sure enough, two Amazons wearing miniskirts and stilettos walk round the corner.

He regains his composure, laughing, That's probably not what you asked me." He recovers enough to talk about the crime story he wrote for Ken Bruen's Dublin Noir anthology. I said, right, this is my license to go mad, and I had a right laugh. It was quite violent and had loads of language." Despite being asked to write an adult novel, he has no immediate plans to do so. I'm doing really well in the kids' books and I'm enjoying it. Being very honest, I don't want to move away from that while it's going so well, I think it would be madness."

The next book in the series is due out in September, so hopefully I'll get it done in time, " he says. After that he has a great ambition to write a classic children's story.

I still love stories like Treasure Island and the Black Arrow and I want to do one of those. That's the one I'm working on at the moment. I want to write a classic boys' adventure story, not a series, just one book that will stand on its own and I can look back in 10 years and say 'that's a ripping yarn and anyone could read it'. I'm still striving towards that. The way I would see it, books like Peter Pan and Treasure Island, everybody knows every character even if they've never read it. I want to create that kind of iconic character." I suggest he may have already created such a character in the criminal teenage mastermind that is Artemis Fowl. Okay, people will remember that character for a while, but you always want to do better yourself and that's what I want to do. This elusive book, maybe it's the next one. We'll see. Once I finish that it will be the next one, " he says laughing. I'll never get there but that's the whole point."

Colfer has enjoyed remarkable success with Artemis Fowl (he has sold six million copies worldwide) and another of his books outside the Fowl series, Half Moon Investigations, is currently on the New York Times bestseller list. ?It's set in Wexford with no magic, except the magic of the people, which is considerable, " he adds, ?a very sarcastic magic. Just like the Dublin magic. They've nothing to insult you with but wit, " he says before telling a story of how, one day, on his way to a restaurant, two youths came up with an ingenious insult. I was walking down the main street and there were these little fellas standing outside the restaurant. They knew who I was but I hadn't got a stupid haircut or anything so they just said, 'look at him with his books'. They got me somehow. They managed to turn that into an insult. It's actually a good thing and yet they manage to get you anyway."

Despite his huge success, Colfer has managed to avoid the glare of publicity and literary celebrity. I just live in Wexford, you know? , " he says laughing. That's all you have to do. I live in Wexford, my family lives down there, if I started being a celebrity, I couldn't take the slagging."

More seriously, he says, I think it's a lot to do with your own personality. I'm not very comfortable in a room full of people I don't know. If I don't know people, I go to the corner. I don't like networking. When I do a show with kids that's fine, I'm in my element there, but once I'm outside the door of the book store or the theatre, it's back to normality for me."

He realises he's sounding a little too selfeffacing and says, I know I sell a lot of books but a lot of people sell a lot of books and there's only a handful of writers you might know. If Terry Pratchett, one of the biggest-selling authors in the world, walked in here without his cape you wouldn't recognise him. You just don't put yourself forward for that." He says he gets a lot of requests by email and does as much as he can but tries not to let it impact on the writing. One thing he always says yes to, however, is teachers' requests for personal appearances. ?All my friends are teachers so they say, 'right you're in my class on Friday and I'm not paying you and bring some books'. And I do it, because otherwise I can't go to the pub anymore."