Stephen Sealey, managing director of Brown Thomas, is one of the sharpest retail minds in Ireland, but over the past ten years I have come to know him also as one of the most modest and self-effacing people I have met.

He is also uniquely placed to say what makes the Weston family, who own Brown Thomas, such successful retailers.

"They are passionate about the product and the business. They are in it for the long term," he said.

It also seems obvious that the family's values remain at the core of the shop's ethos – they are true retailers at heart. Their Selfridges Group, whose managing director is Irishman Paul Kelly, recently bought 12 De Bijenkorf department stores in the Netherlands, adding to the existing four Brown Thomas shops, four Selfridges in Britain and 11 Holt Renfrew shops in Canada.

Sealey is a key player in that business. He enjoys nothing more than walking the Brown Thomas floor and interacting with staff and customers. He is highly approachable and remains open to getting involved in all aspects of the retail business.

But Sealey has also gained experience at the other end of the retail market, with the mass-market Penneys chain. His move to Ireland in 1997, three years before he joined Brown Thomas, was actually to work for Penneys as its buying controller, and he learned a huge amount there from its legendary head, Arthur Ryan.

"I learned an incredible amount but I knew that I wanted to be at the luxury end of the retail business rather than the volume end. My father was in the business, in men's bespoke tailoring, and I knew that I wanted to be in the luxury market too," he said.

He made the move to Brown Thomas in 2000 as buying director responsible for women's wear, children's wear and accessories.

"I joined the business at a good time as I knew Brown Thomas as a customer. I'd been in Ireland for three years before joining the company and had regularly shopped at Brown Thomas. From this perspective I was able to look at the business from the outside in, which allowed for clarity of vision which was not yet corrupted by knowledge of figures.

"I've learned to always write down my thoughts before immersing myself into a new project and that's what I did at the time. You'll find that your views change once you are involved, so you should always write down your intentions before you begin."

It has meant he's not afraid to break with tradition. In 2009, Brown Thomas made Irish history by becoming one of the first shops to open for business on St Stephen's Day. With so much controversy over the decision, I asked Sealey what his thinking was.

"Firstly, it's voluntary for our people to work on 26 December; we ask them if they would like to," he said. "Secondly, it must be acknowledged that there is a changing pattern in Ireland today, and there are now many thousands of non-nationals living here who don't celebrate Christmas and would like to shop on that day.

"We have recognised also that a lot of young people like to gather socially to shop on 26 December. Many of our younger teams would see St Stephen's night as more socially important than the day hours and so are happy to come into work on the day."

This year, the shop seemed set to build on last year's success but a burst sprinkler on the fifth floor of the building caused a flood throughout the shop.

"When the phone rings before the sun rises you know there is something seriously wrong," Sealey said, laughing. He immediately mobilised the staff, decided not to open, and got that message communicated to media and customers instantly, so that by mid-morning the country knew Brown Thomas was closed for the day.

Christmas trade was reasonable. "Pre-Christmas saw a number of factors result in a loss of business, like the snow and ice, and some days saw trade down 30%," he said. "On 27 December we began to claw back the sales. We'll finish the year in a reasonable place, but who knows what might have been if we'd avoided the flood?"

Sealey wishes Brown Thomas was not seen as a shop that caters only to the elite. "I sometimes wish we could hang a sign on the door that says 'We are not as expensive as you think'. There is a perception that Brown Thomas solely trades at designer prices, but this is not the case," he said. "We have a lot of unique and luxurious exclusives at very affordable prices."

Gone are the days of customers battling to get to the till with hoards of goods to buy. Now, retailers have to work harder to entice the customer, sell to them, and give them the kind of brand experience that will ensure they come back. Mary Portas' new reality series, Secret Shopper, emphasises this point as she exposes some of the hopeless customer service on the high street.

At a dinner a year ago in London, Selfridge Group's Kelly discussed with me the importance of quality customer service at that end of the market. It's a point Sealey echoes.

"The three key offerings in retail are product excellence, value, and service," he said. "At the end of the day, there is still money in Ireland: 86% of people still have jobs. The sale process, however, is much more fragile now than before because mentalities have changed. Focusing on service is what will ensure your repeat business."

I asked Sealey if there is a formula for the brand mix of concessions and own-buy labels that make up the floor space at Brown Thomas.

"The most important thing is the edit of brands you have in the store. Ireland is too small to be too elitist," he said. "In our brand portfolio we cater across the board as much as possible. There is no agenda, or rules, when considering own buy, or concession: the driving force is the overall edit.

"We would look at new or emerging brands getting a lot of press and relevant interest. We would then look at existing brands which are not performing very well, and we edit as we see right. The product has to be right, and I believe if you fill the store with what the customer wants you are doing well."

The group's main competition in Dublin comes from Arnotts, which got caught up in plans for its own wider redevelopment.

"The Arnotts and Northern Quarter plans would have enriched that part of the city, there's no doubt about it," he said. "Unfortunately I think it was all a victim of bad timing. I see that Arnotts is strongly focusing on retail at the moment, which is key, but unfortunately, again, their destiny is not in their own hands."

Is there any possibility of Brown Thomas expanding across the Liffey? "Once we've got BT2 back on track, I wouldn't mind a BT2 store there, but it's not a priority," he said. "My vision is about absolute excellence in this shop [Grafton Street]. I'm not interested in expansion for its own sake."

So what about the competition from Dundrum? "Dundrum Town Centre is a great volume destination and we trade successfully in BT2 there. There is a limit, however, as to what can be sold out there," he said. "Customers who want to shop for serious fashion come to the city and come into Brown Thomas on Grafton Street and still have the rest of Dublin city's offerings at their fingertips. The isolation of Dundrum Town Centre can't offer that. Also, we recognise that Brown Thomas is a social venue as much as a shopping destination and this is another unique aspect of our department store."

A subject close to my own heart is the wealth of talent among Irish fashion designers. Sealey supported, showcased, invested in and sold Irish designs at Brown Thomas. At present, Louise Kennedy, Paul Costelloe, Quin & Donnelly, Mary Grant, and Pauric Sweeney are some of the Irish names to be found on Brown Thomas' floors. But to Sealey's mind, there is a fundamental issue to be resolved for Irish designers.

"Too often, Irish designers fall down because of a lack of a business plan, supply chain, and production behind the brand. The talent exists and we do our best to support it. But the label has to be functional as well."

Ian Galvin is chairman of fashion group Aurora Ireland

The Sealey CV

Age: 54

Career: Has worked for Clarks, Penneys and Brown Thomas amongst others

Education: Degree in science from Manchester University

Family: Married with one daughter

Hobbies: Reading, gardening, travel