You don't need to prove blue blood to attend a clan gathering - just the right surname. But the O'Driscolls, when they gathered in Cork, made an exception for Rosita Boland

'Reserved for Chieftain" reads the hand-written sign on an imposing carved chair in the reconstructed Great Hall of Dún na Séad Castle in Baltimore, Co Cork. O'Driscoll chieftains have been coming and going within these historic walls for hundreds of years: the castle, now a private home, dates from 1215.

The present chieftain of the O'Driscoll clan is Dave Driscoll, from Bakewell, Derbyshire, in England. It's the opening of the annual O'Driscoll clan gathering, and Dave arrives to claim his chair in the garb of a 21st-century chieftain. Instead of being dressed in furs and skins and carrying a shield, he's wearing a T-shirt, chain of office, and carrying a digital camera. He's also grinning; no enemies of the clan here today. Unless, of course, foes consist of anyone whose surname is not either O'Driscoll or Driscoll - in which case I am far outnumbered by 132 to one.

The O'Driscolls have been having clan gatherings in this part of south-west Cork for 22 years: their name has long been associated with the locality. There was a huge one-off gathering in 1961, when more than 400 people attended from around the world, and the current style of gathering, over a long weekend in late June, has been going since 1986. The patronym "O" part of the surname often got dropped once families emigrated, so it's all the same whether your surname is O'Driscoll or plain Driscoll. Judy Driscoll from East Lawn Meadow, Massachusetts says, "We call everyone cousin."

But why would you want to travel many miles - from Australia, Canada, the US, and Britain - to Ireland, just to meet lots of other people who have the same name as you, but to whom you are not closely related?

"It's tribal, literally," explains Carol Driscoll, also from East Lawn Meadow, Massachusetts, who is married to Judy's brother, Jim. "Other people don't get it. It's like being part of a community. Ever since I married into the Driscolls, I feel I belong somewhere."

"We say we're Irish-American even if we're fourth or fifth generation," Jim says.

For Neil O'Driscoll, from Brisbane, Australia, this is his sixth time at the clan gathering. In 1880, his great grandfather emigrated from the nearby townland of Woodfield. "Our annual holiday is built around this now," he explains. "These days, we usually start out in America, and we visit the people we've met the previous year at the gathering."

"Somewhere down the line, all of us here originated in this place," says Larry O'Driscoll, from the East End of London, who is here for the second time with his wife Maureen. "You reach an age when you want to know who you are." Larry (75) has roots here that are much closer to the surface of time than many others at the gathering: his father was born on Cape Clear.

The schedule for the clan gathering weekend is like that of a festival; showcasing the area's natural beauty and involving the local community. There are boat trips to the nearby islands of Sherkin and Cape Clear, as well as a sail around Carbery's Hundred Isles. There's a visit to the museum on Cape Clear, music every evening, and a knees-up in the square on the last day, with face painting and entertainment for children. Actually, there is no square in Baltimore, but in the Irish way, that's what the road fronting the harbour is referred to by everyone.

After a while, it strikes me that in many ways, a clan gathering is rather like a large and slightly unruly wedding. There's that celebratory, party atmosphere of family and friends meeting up who don't see each other too often, but who are aware of who's who. There's the exchange of stories about others not present this time. There's a mix of ages: some clan members bring their children with them. There's dancing and drinking and singing. There are speeches. And, like all typical weddings, there are some people present whom it quickly becomes evident are a little less popular, a little more overbearing, and a lot more vocal than others.

There are even two people at the centre of attention - the incoming and outgoing chieftains, Bruce Driscoll from New Brunswick, Canada and Dave Driscoll. A chieftain is elected every two years and is chosen by the local committee that organises the clan gathering. As Marian Bushe (née O'Driscoll) explains: "We try to choose someone who is interested in the history of the clan."

This is Bruce and his wife Marilyn's fourth time at a gathering. His great great grandfather went from Cork to Nova Scotia in 1850. "The gathering is a chance to swap information, trade stories, come back to our roots," he explains.

One of the incoming chieftain's duties is to make a presentation to the rest of the clan. Bruce's presentation, which he makes in Dún na Séad Castle on the history of O'Driscolls in Newfoundland, is outstanding and haunting.

Using archive footage, he tells the story of how the ancestors of many O'Driscolls (and other families) who emigrated from Ireland to Newfoundland were displaced twice over: once, when they left Ireland; and again when they were forced to resettle by the government, from remote fishing communities to newly created, centralised towns. Some of them took their houses with them.

To illustrate this, he shows clips of a documentary made in the 1960s, which depict the extraordinary sight of two-storey houses being towed across the sea from one side of a remote fjord to the other, slightly less remote side. The residents of the house sit in the prow of the boat, their faces immobile as stone. After the presentation, there is a short and sombre silence.

At the clan gathering, everyone is looking for stories about their namesakes.

"I'm not looking for money, just stories," quips Éamon Lankford, director of the Cork placenames survey, who has done a considerable amount of work on the Cork O'Driscolls, despite not sharing their name. He tells the clan that he recently got a letter from the grandson of a woman who had the unfortunate distinction of being the first person to be killed by an automobile in London: "She was an O'Driscoll. I don't know, would you call that a claim to fame?"

Later that evening, when the moonlight is gleaming on the bay, there is an official opening in the square that is not a square. The "official" opening is also very Irish, since the clan gathering actually began the evening before. The speeches are a model of succinct brevity, and the welcome extended to the O'Driscolls gathered in Baltimore's-road-cum square has both integrity and warmth.

"I thought it was either going to be terribly formal or terribly informal and I've found it to be comfortably in the middle," confides Margot O'Driscoll, who is from Birmingham and whose first clan gathering it is. She's come on her own, and she stands among people she does not know, but whose name she shares. For one weekend at least, it does feel as if these people are connected to each other. There's no other word for it, they're truly being, well, clannish.