It wasn’t the first time Celtic fans had come face-to-face with a police riot squad. After the Uefa Cup final in 2003, which the Glasgow team lost 3-2 to Porto, the Spanish police were waiting for them outside the Olympic stadium in Seville.

“They put down their shields and applauded us,” Albert McCready, a Celtic fan from Dublin, recalls. “They couldn’t believe we’d just spent two hours singing, even after we lost.”

The encounter last Saturday in Dublin’s O’Connell Street between gardai and dozens of youths wearing Celtic jerseys was of a decidely darker nature. Fans tumbled out of nearby Celtic drinking haunts to chant “go home, you huns” at the Love Ulster parade, and to throw missiles at gardai.

“It was embarrassing to look at them; it was cringeworthy,” said McCready. “There are people now using the Celtic jersey to show where they come from, and I don’t know how you go about changing that psyche. It is slightly unfortunate, because the Celtic top is prominent-looking at the best of times.”

The green-and-white hoops seem to be turning up in more and more unfavourable situations. In Londonderry, for example, youths wearing Celtic jerseys and carrying tricolours have taken to congregating at places such as the Diamond to barrack loyalist marchers every summer. “They are only there to provoke a reaction and to cause trouble,” William Hay, a local DUP MP, has complained.

Of course all this jersey-wearing is good for Celtic’s bottom line. Half-yearly figures released two weeks ago showed that while turnover was down, due to the club’s losses in Europe, merchandising was up by 48% to £9.6m (€14m). That’s the equivalent of 280,000 replica tops sold in six months.

But even accepting that it is easier to wear than a tricolour, how did it happen that the jersey of a Scottish soccer team is now the way to identify yourself as an Irish nationalist? And given that Celtic fans are famed throughout Europe for singalong good cheer, how come the green-and-white hoops are popping up at nasty sectarian bunfights?

FOR decades, Irish people have been making the pilgrimage to Paradise, the nickname of Celtic’s ground, Parkhead. But 20 years ago, the fans travelling from the republic to Scotland each weekend could fit into a bus. Now there are upwards of 5,000.

McCready, 40, a Dublin office worker, is chairman of the Naomh Padraig branch of the Celtic supporters’ club in Ireland, one of 20 such associations in Dublin alone. When he started making the weekend trips to Scotland in the early 1980s, all the Celtic fans knew each other.

“It was very much a hard core,” he said. “There’s been an explosion of interest in the last decade. The club’s popularity had grown mainly because of media exposure. A key factor was when satellite TV started showing Celtic matches about 10 years ago.”

Then Martin O’Neill from Derry became manager, Neil Lennon from Lurgan the star midfielder, Dermot Desmond from Dublin a director, and the club became successful after years of playing second fiddle to Rangers.

“The Irish fan base has always been important, but it revived significantly,” said Brian Wilson, author of Celtic: A Century With Honour and now a director of the club. “Celtic were in the doldrums for a while. Ten years ago the average Celtic gate was 25,000-30,000. Now you get 60,000 at every home game. The interest from Ireland has gone up too.”

From the dispersion of Celtic jerseys around Ireland, you’d guess this is a youthful and working-class fan base. But organisers say the support is mostly middle-aged and middle-class, even well-to-do.

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