Since 1980, when Paul Costelloe started out, his label has featured the silhouette of a fox running at full stretch, tail flying. Over the intervening years his own red locks (though still longer than might be usual on a 55-year-old with the face and body of a front-row forward) have lost their foxy luxuriance; but as he explains when we meet at his headquarters in Knightsbridge, the logo was never intended to bear any physical resemblance.

"It's an American red running fox. It came from when I was in America and reminded me of my childhood, spending summers in the country and watching my sisters and my brothers hunting and seeing a fox cross the field. I still think it's one of the most spectacular things. I find it sad now to see them walking around Putney and making these dreadful crying noises at night time. But I still admire them. They're survivors."

He has been talking about his recent move to London. For 20 years Paul Costelloe has been Ireland's most famous designer-in-residence, but last September, after many years of weekly commuting, he finally made the break, packed up and shipped out, taking his wife and seven children with him, though he insists his reasons were more pragmatic than sinisterly significant. With Dublin growing ever more popular as a weekend destination ("before it was like getting on a bus, but now, you have to book"), commuting was becoming increasingly difficult. "There comes a time when you think, `my wife's going to be doing that school round for the next 10 years and we're still going to live in the same house then we're going to die'. And I just thought we needed a change of life."

The move should not be seen as reflecting any sense of disillusionment with Ireland, he stresses, nor is it a sign that has he has grown out of being Irish. If anything, being Irish in London is an advantage these days and certainly an improvement on the 1980s when he first started working in London. He recalls sitting in a London TV studio waiting to be interviewed when news came through of a bombing and his guest appearance was cancelled. It happened more than once. Although his Irishness "never came up as an issue" he learnt that "you did not particularly state that you had a Made-In-Ireland label; you had to be somewhat discerning as to your marketing practice."

Perhaps this unease contributed to Costelloe's refusal to be pigeon-holed as an Irish designer. His horizons were always international; but while success in Ireland and the UK came quickly and remains firm, the ultimate prize, the market he always had in his sights, continues to elude him.

"If you're going to crack the American market I really believe you have to tie up with an American company. It's very hard. Very few Europeans have succeeded without enormous expense and investment." Only the Italians have the measure of it, he says, and they are totally committed, working seven days a week.

In 1997 Paul Costelloe went some way to improving his chances of global success when he sold his company to a British consortium, staying on as design director. His name, however, remains his own. There have been too many stories of designers being sold down the river he says. "I own the one thing every designer must not lose: the rights to his name. You are like a footballer to a certain extent, you may not be in the premier league but as long as you are still kicking the ball, you can still get a job."

Paul Costelloe has never been someone for whom standing still and holding his hand out was an option, and this month sees the launch of his earthenware collection for Wedgwood. It's classic Costelloe: simple, elegant, generous and big (your man is a mighty six foot four) with a lustrous glaze reminiscent of early T'ang dynasty ceramics. Although Costelloe admits to knowing nothing at all about pottery, he is very proud of what has been achieved - the striking glaze on the inside of the vessels is a first in the world of commercial production, he believes, and was brought about through sheer persistence.

"I wanted to get the texture of the linen and yet retain the subtlety of that sheen, and they really were great: sweet, wonderful Stoke-On-Trent people, a very young creative team and they pushed the production to develop it."

For all Wedgwood's English heritage, the company, he points out, is now Irish, wholly owned by Waterford. "It's wonderful to be part of the success. I've known failure - everybody has - and you have to have known that to appreciate the good times."

There have been the usual commercial set-backs - losing out on a licence or corporate contract - but the Costelloe star suffered a particularly public eclipse in 1998 after Image magazine devoted an issue to Ireland's 90 most stylish women. Asked to comment, Costelloe was quoted as saying that, although Irish women had many great qualities, style was not one of them. The outcry from media and women alike was deafening, and took him completely by surprise.

"I take the good with the bad, and if something ends up being slightly twisted in some form, you say, fine. And I do think [the journalist] milked me. He basically brought me up an alley and he did a hell of a job and I thought, `Okay, let it go. It's a bit of a laugh.' But then, Wham! It all happened. But I do think we should be able to laugh at ourselves and I do think that these Irish women are taking themselves very very seriously. The nature of the Irish beast is to have humour. As soon as we start becoming precious, then forget it."

The story had little effect on any commercial level, he says. Indeed in Killarney and Kerry, sales rose appreciably. But the issue continues to dog him. "Only a month ago I was talking to my accountant in Bewley's new hotel in Ballsbridge when this attractive blonde walks up to me, black suit, mobile in her hand and lays into me. And I thought she was going to say something nice. I mean, it was two years ago. Give me a break." Although he says this sideshow had nothing to do with his decision to move to London he adds: "That's what I like about London - nobody gives a shit."

Paul was the youngest of seven children. The reason he now has seven of his own (six boys, one girl, aged six to 18) was simply to match his Da, he says with a twinkle in his pale blue eyes. ("It was a bit of a challenge, a bit of an ego thing, I think. It certainly wasn't the church or religion. I was just a bit gung-ho macho.")

His father was managing director of traditional rainwear manufacturers, Valstar. The family were "well-to-do by Irish standards," he explains. "We had a lovely big house with a croquet lawn, tennis court and fields." And that image is still the one he dreams of, the palimpsest beneath his clothes. "I think of it like a painting. There's nothing more beautiful than a girl - and I'm particularly thinking of my wife - when she wears a white linen, longish dress and a pair of plimsolls, lightly tanned and she has just got her hair washed and you're walking on a beach. It is most beautiful. It is feminine." (He pronounces it to rhyme with feline.) "It is not overtly sexual; it's truly feminine."

When Costelloe was growing up, all he ever wanted was to be a painter. But when it came to choosing a career, his brother Robert, older by a year, had already taken the artist niche in the family pantheon. It would have to be something different. When this "tall, lanky, lusty Irishman" emerged from the chrysalis of Blackrock College with no other interest, he claims, beyond "what any 17-year-old thinks about 70 per cent of the time", a job which involved regular proximity to women certainly had its attractions. And with his father in the garment trade, it was an acceptable compromise, though he still thinks of himself primarily as a painter rather than a designer.

First stop was preliminary training in Paris, followed by an apprenticeship in the atelier of Jacques Esterell, ("Paris is a wonderful place to mature, though I wouldn't say grow up. I don't think I've ever grown up"). Next came a spell with Marks & Spencer in London, then another, if classier, chain store, La Rinascente in Milan. New York proved a dead end, so in 1977 he returned to Dublin, a mature and experienced 32-year-old with "a smattering of half-learnt languages" and an intimate understanding of cloth, particularly linen.

Paul Costelloe's near-evangelical espousal of Ireland's famous export was largely responsible for transforming its image from that of sheets, tablecloths and priestly vestments into must-have fashion chic, as sported by Costelloe's most famous client, Diana, Princess of Wales. "It has always been an elitist fibre, an aristocratic fibre. Jesus Christ was wrapped in linen, and it's always been a material used by the church, different churches. There is still only a tiny amount of linen worn in the world, but it wears brilliantly; the more you wear it, the more you wash it, the better it looks."

When it comes to cloth, Costelloe never leaves the selection to anyone else. It's the key to his success, he says. That and keeping in touch with what's happening in the high street, and in Italy, "keeping a sense of humour and being able to laugh, to talk, to communicate. And being honest. Trying to be honest."

Six months on, the move to London is proving invigorating, challenging and fun, he says. "Oddly, although Anne and I have been married for a long time, we have never really lived with each other. Now she sees me nearly every night, and it's `Oh my God, not you again'. But she's from north Dublin, so she can handle it."

"It keeps you edgy," he explains. "It resparks energies that you thought you had lost and it's also a humbling experience. In Dublin I'm known. In the local supermarkets, I could say, right I'll pay you when I get back. Here I go into my local Sainsbury's - they say we'll mind your basket until you come back with the money."

Costelloe's work has at least remained a constant. For his wife, without this anchor, the move has been much more difficult: 15 years younger than her uxorious husband, she has never lived anywhere else. Then there are the inevitable complications of such a large family's schooling, though all are settled now: his daughter at an all-girls school in Chelsea, the two youngest boys in Putney, the next up in Battersea, two boarding with the Benedictines in Ampleforth, Yorkshire and the eldest in Italy, where he's enjoying a gap year teaching rugby and is "supposed to be learning Italian".

In reply to my asking if the remnants of his fox-like hair are destined for a pony tail, the big man laughs. No, he says. It is simply his last hurrah - "like Spencer Tracy in The Last Hurrah, the last time he runs for mayor". As for putting it in an elastic band, he roars with laughter. "Do you think my children would allow me to do that? You must be joking. Children can be very honest. They don't give me an inch. But they're great, the fruit of life. Any man who hasn't had the luxury of a child has missed out definitely; and anyone who has one or two and doesn't appreciate it is a fool."

And now he's rushing off. An important engagement and one he daren't be late for: his son William's First Communion. ("The Catholics are much more intense here, much more involved.") His parting shot as he turns tail is: "You won't see Armani or Donatella doing that."

Paul Costelloe's Wedgwood range is available exclusively in Brown Thomas, Grafton Street, Dublin