It is enough to make a southern publican weep. Morning, noon and evening, eager shoppers from the 26 counties are pouring into Northern supermarkets, and wheeling out trolleys full of drink to their cars.

With the euro soaring against sterling, the steady flow of shoppers over the border has turned into a flood over the past few weeks, helping to transform Newry into Ireland's last boomtown.

And the North's good luck is the misfortune of Dundalk and other border towns in the South; on an average shopping day, they are largely bereft of people. In the centre of Dundalk, 'To Let' and 'For Sale' signs adorn shops.

One local businessman in Dundalk was aghast at the effect of cross-border trade on the town: "It's crazy. Sometimes the queues of shoppers going over the border are six miles long. The centre of Dundalk is dead, because everyone is going North.''

A Sainsbury's manager told me the chain's supermarket in Newry, only a few miles from the border, now sells more alcohol than any other Sainsbury's store in the world. Overall sales are up by 70 to 90pc this year -- largely due to the Southern invasion.

A glance at the prices offers an instant explanation. A large bottle of Irish whiskey, distilled in this jurisdiction, costs nearly €14 less on the other side of the border. Popular wine labels are not much more than half the price of their Southern equivalents.

The cross-border shopping mania is not just about drink, however. According to the manager, the Newry Sainsbury's store also notches up the highest sales figures in the chain for baby products and confectionery.

Young parents with babies are going north just for the nappies. Visitors such as Bernadette Edwards from Swords, Co Dublin have become regulars. Last week she went up and spent €300. And this week she was back again. With improved roads, and wildly different prices, Newry is becoming a shopping centre for north Dublin.

The scene in the aisles in the supermarket occasionally borders on pandemonium, as Southern invaders pile up their trolleys to unmanageable heights. Dublin voices abound.

I approached one tweedy lady with a Dublin 4 accent in Sainsbury's. She must have had 40 litres of Jameson in her trolley, but she was not keen to talk. Others headed to the car park with enough wine to keep a family tipsy for a year. Many Southern visitors needed three or four trolleys to carry their purchases.

The cross-border invasion and a further rise in the euro this week comes as a survey predicted that Christmas sales figures would be down 10pc in real terms in the South this year.

Few shoppers are inclined to heed the call of Dublin's Lord Mayor Eibhlin Byrne who said a week ago that all citizens should show some "civic patriotism'' and do their Christmas shopping at home, rather than spending on trips to New York or the other side of the border.

This call to patriotism is greeted with scorn by Southern shoppers when it is mentioned.

Barbara Delaney from Ardee, Co Louth says: "How can politicians expect us to shop in Dublin when the prices are just much too high? It is the fault of politicians that we are in this mess. How can they call it patriotism? We're all on the same island.''

Southern politicians have tried for centuries to unite Protestants, Catholics and dissenters, North and South. Shopping has done more than anything to bring us together.

The King family from Blanchardstown in Dublin were making a few savings, but were also enjoying the day out. Cross-border bargain hunting has become a pastime.

Jeffrey King, who is not a drinker, said: "I thought it would just be a nice trip. It is 30 years since I have been up here.''

Calls to patriotism by Dublin politicians do not cut any ice with Cathal Austin, manager of the Quays shopping centre in Newry. The town's fortunes have ebbed and flowed over the years.

"Newry has been through some bad times as well. I remember when I was growing up in the 1980s, the shoe was on the other foot. We used to go shopping in Dundalk in places like Penney's and Dunnes Stores, because they were cheaper then.''

Price is not the only driving force behind Newry's retail boom, according to Cathal Austin.

"The end of the Troubles made a huge difference because many shoppers had been reluctant to come North. The improved roads have also been an important factor. It only takes an hour to get here from Dublin.''

The head of Dundalk's Chamber of Commerce, Bill Tosh, warned that cross-border shopping is not just a local issue affecting traders close to the border. It is also damaging the Irish economy. "Millions of euro will be lost to the Exchequer in the run up to Christmas because of it,'' he said.

Although all the shoppers I met were buying for their own personal use, Mr Tosh believes buyers from the hospitality industry in the South are also snapping up drink in supermarkets in the North in order to evade duties.

In a forthright letter to town councillors in Dundalk, Mr Tosh said the town was facing a dire scenario: "We are like rabbits caught in the headlights and we don't know where to go to next.''

Like most businessmen and women in the town he does not blame his fellow townspeople for going North. He says basic foodstuffs in the South are "over-priced and totally unaffordable''.

Bill Tosh wants the Government to investigate the huge discrepancies in prices between the North and the South.

He also believes there should be a clampdown on businesses who import alcohol from across the Border. "There may be some differences in costs for retailers between the North and South, but that does not explain the vast gaps in prices.''

Politicians may don the green shirt and urge us to shop close to home, but this plea will almost certainly fall on deaf ears as the recession deepens -- particularly when the Irish soccer shirt costs €10 more on this side of the border.