United we stand is the maxim for most Irish team sports, although this excludes volleyball, which has separate governing bodies in each country.
Rugby union is the most famous all-Ireland sport, with players from the north and south pulling on the same jersey in the Six Nations and other internationals as well as an integral part of British & Irish Lions' teams.
Hockey is united but, once you have declared for the Irish team, not even northern players can switch and become part of a Team GB at the Olympics. "You can't get two bites at the cherry," said an Irish Hockey Association spokesman. Basketball Ireland covers players in both countries, as does Cricket Ireland.
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In mainstream individual sports such as athletics and swimming, though, competitors have to choose, although there is a fair amount of cross-border traffic. James McIlroy, who announced his retirement last month, was fourth in the 800m at the 1998 European Indoor Championships. He lived in Larne where he dared not walk the streets wearing his Republic of Ireland tracksuit, or even hang it on his washing line, so he switched allegiance to GB. Earlier he had been an under-18 Northern Ireland footballer but, when they ignored him, he went to the Republic.
Brian Doyle, the Cumbernauld sprinter who formerly ran for Scotland, switched to Ireland.
Because of inter-marriage between north and south, it is very common for sports people on either side of the border to be dual-qualified.
Barry McGuigan, the former World Boxing Association featherweight champion (left), played musical chairs with nationality. He won bantamweight gold for Northern Ireland at the 1978 Commonwealth Games in Edmonton, and then boxed for the Republic two years later in Moscow. He was soon British again, though, upsetting some when he won the British featherweight title.
Another boxer, Wayne McCullough, did likewise. Raised in the Shankhill, he won Auckland Commonwealth gold as bantamweight for Northern Ireland in 1990, then Olympic bantamweight silver for the Republic two years later in Barcelona. The former World Boxing Council and World Boxing Organisation champion is now a US citizen.
The Formula One driver Eddie Irvine (right) was British but held an Irish driver's licence, so the world governing body, the FIA, issued him with an Irish super licence. At his first podium - he was third in the 1995 Canadian Grand Prix - the Union flag was flown. For his third (second at the 1997 Argentinian Grand Prix) the Tricolour went up the pole. His family consequently received threats from both sides of the sectarian divide, so Irvine requested a politically neutral shamrock be flown, and the non-sectarian Londonderry Air be played. The FIA refused and subsequently a Union flag and Tricolour appeared on alternate visits to the podium.
Darron Gibson of Manchester United, who is currently on loan to Wolves, was born in Derry. He played under-16 for Northern Ireland but, under the Good Friday Agreement, individuals can opt for citizenship of either country. Gibson has now been capped by the Republic.
FIFA say this is against their rules, leaving a question over whether national Good Friday legislation takes precedence, or FIFA rules. The Irish Football Association, Northern Ireland football's governing body, want FIFA to rule in their favour, which would leave the potential for legal challenge.