Ballykissangel is turning into Milton Keynes

Another St Patrick's Day is looming. Guinness advertisements are appearing on English bus stops. Sentimental American associations called things like the Ohio Shamrock Guild will parade through the streets of Dublin on Friday, while thousands of real Irish people will be making their way home, with sore heads and empty pockets, after the Cheltenham Gold Cup.

These things have been happening on St Patrick's Day for decades. But they obscure the fact that the Republic has been through the most remarkable change in identity of any country in Europe. It's more than the much-vaunted "Europeanising" of its currency, its road signs and its commercial outlook. It's a whole shift in expectation, in what the Irish people consider valuable.

Ireland's chief export used to be its children. In my parents' generation, and to some extent my own, it was taken for granted that the young, after completing their school career or college degree, would choose which country to relocate themselves in. There were so few jobs in the depopulated rural west, they had to find work in exile.

At the time Ireland's culture was hermitic - fluting melancholic music, diddly-dee fiddles, stiffly hopping dance routines, twinkly crooners who won Eurovision Song Contests, hopeless fashions, grotty shops, peasant food, a game played with an ash machete, priests, nuns, clay pipes and craven deference to the Church of Rome - and its consumers didn't care to assimilate with the new stuff in London or San Francisco.

Then it all changed. In the last 15 years, Irish culture became the nation's biggest export. The Irish invaded the rock world (U2, the Pogues, the Corrs), folk music became trendy, step-dancing became the biggest box- office draw on the planet, no matter how fake and Flatley-fied it was. Ballykissangel became a kind of lost Arcadian hometown for British viewers.

The economy boomed. And as foreign information-technology firms kept investing in Mayo or Kerry, two rumours about the future could be heard in the new Republic. One was that, if more jobs became available, Ireland's children needn't be exported any more. And a second whisper said: Ireland, long a distressful nation of people saying goodbye to their youth, might, to its amazement, start offering jobs to foreigners. An emigrant culture could become an immigrant one, welcoming the world through its doors.

But success is achieved at a cost. Now more Irish are staying at home, the country has been plunged into a ferment of property speculation. My father's hometown of Athenry (1998 population, 1,500) has doubled in size in two years, while 140 acres of farmland have been re-zoned to take another 2,000 houses. With building land currently worth pounds 110,000 an acre, no farmer is likely to stress the importance of crop rotation.

Locals are alarmed by these developments. They complain that no thought has been given to planning, to the culture of small-town life. My brother- in-law, a vet, is rung up by new arrivals asking his address. It's the first time this has ever happened. "People in town used to know where the vet lived. Now I'll have to put up a sign..."

By a heavy irony, the chief result of a booming economy and a sparkling reputation in the eyes of the world has been to turn some parts of Ireland into a nightmare of ribbon housing and overpopulation. For the first time, the inhabitants' children will be able to stick around, and find jobs and be near the sights and sounds, the streams and mountains of their youth. But what will become of the small towns when the innocence, the hermitic life, is lost? What will be the point in staying on, when Ballykissangel turns into Milton Keynes?