This time it's Brian Lenihan's turn to do his patriotic duty. When he tried to discourage us from cross-border shopping last year, on the grounds that we'd be paying "her majesty's taxes" rather than contributing to the Republic's economy, his reproach fell on deaf ears.

The only person won over by his rhetoric was Tanaiste Mary Coughlan, who parroted the same forked tongue message last week.

Have her words had any more impact?

They've been as effective as the little boy's finger in the dyke, judging by the traffic on the M1 -- which is thick with cars driving northwards to buy more competitively priced goods.

But people are not setting out to commit acts of patriotic sabotage. They are trying to make ends meet. When cash is tight, balancing the household budget comes ahead of any 'ism' -- even patriotism. Or trade unionism, for that matter.

On Tuesday we saw how the lure of low prices proved too tempting for striking public servants who swapped their banners for shopping baskets causing five-mile tailbacks on the road to Newry.

So, if the Finance Minister wishes to discourage so-called unpatriotic deeds, he can do something about it. He can trim VAT in the Budget. Something constructive needs to happen soon or the only shops with their lights left on will be Two Euro emporiums. Even then, we're probably the only European country where costs are so high we can't stretch to One Euro shops.

Whenever I travel over the border to visit family, it's as if I haven't left home in Dublin. On the contrary, a sizeable proportion of the Republic piles in behind me.

Once, you used to be able to tell you were in the North because men with rifles in their arms and twigs in their helmets would flag you down. Now, the difference is the price chasm.

Northern shops are crammed with visitors with southern accents, the car parks nose-to-bumper with southern registrations, and euro notes are nearly as commonplace as bills with the Queen's head on them. Euro transactions are so routine, it's almost as if Stormont voted to secede from sterling.

Just the other day I stood in a shopping centre in my home town of Omagh, dazed by the volume of this seasonal boost to traders' tills. Last year was busy but this year is manic, led by favourable exchange rates, gentler VAT and excise duties, and a lower cost environment.

If shoppers are converging on Omagh, 20 miles north of the border, and lacking either Belfast's variety or the geographical advantages of border towns such as Newry and Enniskillen, then they must be swarming all over the six counties. And one man's gain is another man's loss -- or as Erasmus commented 500 years ago: "Lyghtly whan one wynneth, an other loseth." Yet who can blame people for shopping around and spending their shrinking resources where they get best value?

I saw children's toys, play station games, electrical goods and clothing being bought. But above all, there was alcohol -- enough to drown a nation's sorrows. At least temporarily.

The supermarkets flag up offers which shoppers find irresistible. Gin or vodka for £10, three bottles of plonk for another tenner; prices which work out even more affordable with sterling hovering at around 90p per euro. And as shoppers stockpile festive cheer, they lob in other supplies -- from washing powder to disposable nappies.

The chemist chains are just as crowded as the supermarkets -- certain medicines are considerably cheaper, while Superdrug and Semi-Chem acted like a magnet with their boxed perfume sets, sticky-sweet scents from the likes of Kylie and Alex Curran aimed at teenage girls.

The shoppers I watched were utterly focused. They produced their mobile phones and rang friends in other shops to alert them to mark-downs, or contacted relatives offering to pick up some booty if a bargain caught their eye. One woman used her BlackBerry to go online and do a price comparison on a toy she was holding. Elsewhere, a mother lifted a tin of chocolates, until her daughter told her to put them back because Asda was running a special offer of two tins for £7.

Asda was a mecca, but shoppers also thronged Next and Marks and Spencer, both with southern branches unlike the supermarket giant. So it's not as if they were looking for goods unavailable at home. What they wanted was bang for their buck.

Northern retailers are ecstatic, but some locals have started muttering. No spaces in the car parks. Queues at the tills. Stocks in shops running low. There was particular vexation about Go Go Hamsters selling out -- a furry interactive 'pet' which is this year's must-have. "Southerners nabbed my daughter's toy," complained a parent -- as if Vikings had raided the store.

But southern trade is giving the North's economy a fillip and, as I remind my relatives, aren't they the lucky ones not to have to trail the country in search of value?

Politicians need to do something more constructive than quote dulce et decorum est to keep retailers above water. VAT cuts could give them a stimulus, while rent and rate reductions should also help.

Retailers need to stir themselves, too. Twinkly fairy lights aren't enough to coax people to spend during a recession. Dropping prices works -- some shops have done it already, but not by enough. I walked around Dublin city centre the other day and admired the lighting displays, but they were no incentive to pay over the odds for items I can buy cheaper in the North or via the internet.

This cost-consciousness isn't just a Christmas phenomenon. It's a whole new mind-set.

mdevlin@independent.ie

- MARTINA DEVLIN

Irish Independent