Sport often reveals true feelings about national loyalties. When the Scotish watch an international game, their allegiance is usually to "anyone but England".
But when Rangers play Celtic, which side raises a Scottish nationalist flag? Neither. Rangers considers itself "British" and flies a Union Jack while Celtic is characterised as Irish, and flies the Tricolour.
The sovereignty of a nation is complicated, as Alex Salmond and his ScotNats will surely find out. And a largely unconsidered angle in the looming referendum on whether the United Kingdom will break up if Scotland becomes independent is the impact on Northern Ireland.
Ulster Unionists have always championed the union of Great Britain and Northern Ireland, but their more particular attachment has been to Scotland rather than to England.
The late Ulster historian A T Q Stewart showed in his research how close the links were between Northern Ireland and Scotland, dubbing those 33 miles of water between the two "the narrow ground". In mediaeval times, when land was thickly forested, it was easier to sail between Larne and Stranraer than to penetrate forest.
So it is an old bond. The university that Ulster Protestants most aspire to is neither Queens in Belfast nor Trinity in Dublin, but St Andrew's in Scotland.
But if Scotland should quit the union of Great Britain and Northern Ireland, where does that leave the Ulster Unionists?
Orphaned, basically. If their closest kinsmen within the United Kingdom spurn the UK, they are out on a limb. What would remain would be England and Wales, as one devolved entity, and a separate Scotland.
The referendum that could detach Scotland from England is set for 2014. If Alex Salmond cannot be sure of a "yes" vote for Scottish independence, he and his able deputy Nicola Sturgeon are nonetheless riding high in confidence and a growing awareness of Scottish identity.
The break-up of Scotland and England is being likened to a divorce, or possibly an agreed separation. Divorce means total dissolution. The other option, "Devo Max", or maximum devolution, would be more like a civilised agreement for the partners to live separate lives.
Total separation means full Scottish autonomy, and the end of the UK. "Devo-max" is Home Rule -- Scotland having much greater control over its own affairs, but retaining the Crown, attachment to sterling and shared British institutions.
Again, where does all this leave allegiances in Northern Ireland? Some moderate Ulster Unionists have traditionally seen themselves as both Irish and British (and they cheer for the Irish rugby team). But if there is no such thing as "British" any more, where is the Ulster Unionist identity?
The break-up of a political union is no small thing, because treaties, customs, languages and cultures get knitted together over the centuries and there are shared memories, which go way back -- the Highland regiments fighting for the Crown, or the extraordinary number of Scots who were the engineers of the British Empire.
There are celebrity endorsements on both sides, with Sean Connery, painter Jack Vettriano and novelist James Kelman as the best-known advocates for Scottish independence, while Billy Connolly and Ewan McGregor reject such "narrow nationalism".
Labour voters in Scotland are more opposed to nationalism, and maintain a historic sense of solidarity with their English comrades.
Yet for all his confident talk of an independent Scotland, Mr Salmond can be cautious. He no longer boasts about the "arc of prosperity", which would range from Scotland to Ireland and Iceland. Irish independence, though democratically supported, was bought dear -- and, in the end, total sovereignty usually eludes small nations.
Mr Salmond and Ms Sturgeon are proud of the generous welfare state Scotland offers -- free universities, free care for the elderly -- but once they control their own revenues entirely, they will find that budgets have to be met. Even if they claw back the revenues from North Sea oil, they will miss the subsidies that come from England.
There is one opportunity that the Scottish referendum could open for Ireland: maybe now is the time to claim Rockall, that set of rocks between Ulster and Scotland beneath whose base lie rich deposits of oil.
If "Britain" ceases to exist, Rockall surely qualifies as Irish territory. But which flag will it fly? The Tricolour or the Red Hand of Ulster?