TWO weeks ago the London Times Diary noted that former Defence Secretary, Michael Portillo, was seen indulging in a little shopping therapy at Thomas Pink, "fingering a shirt in fuchsia Prince of Wales check".

Always a snappy dresser, Mr Portillo knows where to go for that little extra zip. Other Jermyn Street names may have the patina of age. Thomas Pink has the bloom youth. Other customers include Viscount Linley, Hugh Grant, John F. Kennedy Jr and Elle McPhearson. Jermyn Street is to shirts what Savile Row is to suits, with traditions and names to match. But it took brothers James and Peter Mullen, from Rathgar in Dublin, to bring some fresh air into the rarefied atmosphere without sacrificing quality for price.

Within 14 years of opening its first shop, Thomas Pink is the dominant brand in the premium sector of the UK shirt market. In July, its opens the first Irish branch in Dublin's Dawson Street.

"We've thought about Dublin before; we weren't absolutely confident it would go well, but now we are," says James Mullen. "It was just a matter of timing: the fact that there are more people there than five or 10 years ago who are prepared to spend In ore than they would have on a good quality shirt. Also, it's pretty important from our point of view to get up to a critical mass level. We now have 14 outlets in the UK. There are absolutely no economies in having a shop in another country. But we feel big enough that we can start stepping overseas and obviously Dublin is semi overseas

James Mullen read law at Trinity, then did a business degree at UCD. He set up a launderette business in Dublin, then came the shirt idea. "It was just a market opportunity. We did very little actual research. We just realised there were a lot of people our age, in their twenties, who were now working in serious jobs in London and wanted to look smartly dressed, but couldn't afford a very expensive wardrobe. So the initial idea was to undercut all the Jermyn Street people, possibly by cutting corners. Then when we started looking at the prototype shirt, we realised there was no point in cutting corners, that it would just limit market."

Traditional Jermyn Street shirt-makers, Mr Mullen explains, were not maximising their pole position on the retail grid. "It's a reasonably simple idea. You have a shop that's filled with shirts and as long as the shirt is properly made, as long as the product is good from the beginning, the rest is a matter of laying it out nicely and making sure you price properly and promote properly. And a lot of those other people, they make nice shirts, but after that kind of give up. As far as they're concerned: "we've made a nice shirt, it's up to the customers to find us now."

The Mullen brothers weren't entirely unfamiliar with the world of shirts. Their father was a shirt manufacturer in Dublin, and at the beginning, the family factory did make shirts for them, but it was a steep learning curve.

"It took a while for them to do it properly because they were used to mass market stuff, producing thousands every day for people like Dunnes Stores. And we said, `Hang on. You've got to slow right down. You've got to get many more stitches in', and it took them a while to sort that out."

The whole process of making a good quality shirt is much more complicated, says Mr Mullen. "A cheaper shirt doesn't have that much work in it. And it starts with the fabric. If you're using a good fabric you should put it together properly." The cotton is two-fold poplin, grown in Egypt or the Sudan, spun and woven in Italian mills, since the Lancashire mills closed down soon after Thomas Pink set up shop. There is no longer a family manufacturing connection, but Thomas Pink shirts are still made in Ireland. "We have one factory in Donegal and the rest in the Six Counties."

The name comes from a famous 18th century tailor who "made the best hunting coats that money could buy" so: "hunting pink" and "in the pink". Tradition is as much what Thomas Pink sells as shirts. But there is nothing traditional in the way they sell, which James Mullen describes as "a shirt buying experience".

"To a large extent we have just broadened the market. The people buying from us now didn't really give thought to buying shirts. They bought them in a department store. Now we've turned up and said this is something you should pay attention to."

The first Thomas Pink shop, opened in 1984, was not in Jermyn Street, but in Chelsea backwater, sited opposite a popular cinema. It's a lesson they have not forgotten. "We can afford to be in slightly secondary positions because the sort of customers who come to us know what they want and as long as we advertise, as long as it's still very convenient, it works. The Dawson Street location in Dublin is perfect from that point of view. We don't have to be in the middle of Grafton Street with all the other really busy shops. Because people will come to us.

And it seems they do. Last week their customer-friendly Jermyn Street flagship branch was busy, very busy. Far more so than any of their old neighbours.

And what does their father think of the Mullen sons' success? "He finds it all quite amusing and quite extraordinary," says James Mullen wryly. "It's the shirt business, but a completely different end of it. He doesn't really understand and I think he's just waiting for everything to fall apart at some stage." In September, after the opening of the Dawson Street shop, comes New York. Old Mr Mullen will have a long wait.