It’s a sign of the times when the DUP and Sinn Fein are both championing an all-Ireland economy, while the Irish government is railing against cross-border shopping.

The lower price of alcohol in the north has long been an incentive for southern shoppers who want to stock up before Christmas, but now the plummeting value of sterling against the euro means nearly all goods apart from diesel are cheaper in Northern Ireland. Last week the north’s advantage was compounded when Alistair Darling, the British chancellor, cut VAT to 15%. Meanwhile Brian Lenihan, his Irish counterpart, increased it to 21.5%.

Northern border towns such as Newry and Armagh have become shopping meccas with up to 40% of retail sales being made in euros. Castleblayney traders estimate that business is down 30% as a result of the exodus. Most big shops as far north as Belfast will give prices in euros. Some offer good rates of exchange, for instance £1 equals ¤1 in a toy store in Newry although the official exchange rate is 84p.

Nor is there an end in sight, with economists predicting that sterling will fall by at least 3% in the coming months. There is even talk of a run on the pound, which could bring parity with the euro and make goods cheaper still. Small wonder that Belfast city-centre businesses have joined forces to stage an advertising campaign in the republic.

It’s all a bit much for Lenihan. “When you shop in Northern Ireland, you’re paying Her Majesty’s taxes; you’re not paying taxes to the state that you live in,” the Irish finance minister stormed, sounding a bit like Ruairi O’Bradaigh of Republican Sinn Fein. Lenihan called on shoppers to do their “patriotic duty” by spending their euros south of the border.

He wasn’t alone. Jim Power, an economist, described cross-border shopping trips as “the ultimate act of patriotic sabotage”. Power appealed to consumers to use their spending power to safeguard the jobs of their families, friends and neighbours — which do not seem to include the foreigners north of Dundalk.

Talk of patriotic shopping is a long way from 1916, as Gerard O’Hare, who owns shopping centres on both sides of the border and sits on the board of InterTrade Ireland, noted.

By comparison Ulster’s strange bedfellows, the DUP and Sinn Fein, are solid in defence of the island economy. Changed days since Ian Paisley ran a campaign against the acceptance of Irish punts in the north under the slogan “We don’t want your Mickey Mouse money”.

Nowadays the DUP takes a more cosmopolitan attitude and is even lecturing the Irish authorities on their narrow, partitionist attitudes. “It is interesting that the Irish government supports a united Ireland, but when it comes to patriotism that only extends to the 26 counties,” said an outraged Jeffrey Donaldson, a DUP minister in the executive.

“People will travel almost anywhere to get a good bargain,” chipped in Martin McGuinness, whose home town of Londonderry is a prime beneficiary of the cross-border shopping exodus from counties such as Donegal, Sligo and Leitrim.

Martina Anderson, a Sinn Fein MLA in Derry, who has done time for bombing England, now sees no problems with taxes going to HM’s Treasury. She urged Lenihan to “re-evaluate his government’s poor economic policies and fiscal priorities” and to stop “making off-the-cuff excuses that shopping in the north is costing the Irish exchequer”.

Peter Robinson, the first minister, even congratulated the Irish government on building such good roads on which to carry the shoppers north.

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