When Scotland voted on independence in September 2014, Nicola Sturgeon, then the deputy leader of the Scottish National Party (SNP) and now its leader, described the referendum as a "once in a generation" event.

I suppose the definition of "a generation" is flexible. To Sturgeon, it evidently means "four years": She now wants another vote next fall.

What has changed? Not public opinion. The polls have barely budged since the last referendum, which resulted in a 55-45 vote against separation. Scots are an admirably bloody-minded people and, when asked the same question, they tend to respond the same way, only with added emphasis. Fewer than one in three Scots favors a second poll, and the SNP's insistence on one strikes even pro-independence voters as the act of a bad loser.

Sturgeon justifies her volte-face by pointing to last year's European Union referendum, in which England and Wales returned Leave majorities, while Scotland and Northern Ireland voted Remain. She insists on seeing Brexit as a product of English nationalism — something supposedly alien to goody-goody, Left-of-Center, cosmopolitan Scotland. And, in fairness, there was a divergence in the vote — though you'd never guess, listening to the SNP leader, that two in five Scots voted Leave.

Still, the idea that Scotland is somehow a more intrinsically European place than England is fanciful. When the previous European referendum was held, in 1975, the Scots voted to withdraw in far larger numbers than the English.

The truth is that Scotland and England share most of the attributes that usually define national identity. We speak the same language, watch the same TV, shop at the same chains, follow the same sports, eat the same unhealthy food, talk in the same sardonic tone.

The elemental case for union was made by its first champion, King James VI of Scotland, who, on the death of his cousin, Queen Elizabeth, also became King James I of England. In his first address to England's Parliament in 1604, speaking with a heavy Scottish accent, he observed that the border between his two realms was accidental rather than ethnographic: "Hath not God first united these kingdoms, both in language and religion and similitude of manners? Hath He not made us all in one island, compassed by one sea?"

His Majesty was right. There was a cultural frontier in Great Britain, but it divided the Highlands from the rest of the island, not England from Scotland. Lowland Scots felt more kinship with their fellow English-speakers than with the wild clansmen from whom they were sundered by faith, speech and custom. Highlanders, for their part, used the word "English" or "Sassenach" (Saxon) to describe both Lowlanders and Englishmen, making no distinction between them.

Forget what you saw in "Braveheart." Scotland was not annexed by its larger neighbor. If anything, it was the other way around. When James VI inherited his second kingdom, Scots swarmed south with their monarch, snapping up lands and titles. The English felt almost as if they were being invaded, and resentfully refused to grant James the title he craved, "King of Great Britain." It took a century before the two parliaments were merged — again, provoking furious resentment in England.

Scottish separatism is in a different category from, say, Kosovan or Kurdish or Chechen separatism. It isn't based on ethnic or linguistic identity. Rather, its chief appeal is political: Break away from England, the argument goes, and you'll never get another Conservative government. This is true enough; but it is already being addressed by more devolution of powers, especially over taxation.

The idea that Scotland is somehow held down is contradicted by the recent referendum. Not one U.K. politician tried to deny that Scots had the right to walk away. The same would not be true if, say, Corsica wanted to leave France, or Sardinia, Italy. When Catalonia organized an independence referendum two years ago, its leaders were put on trial. I also seem to recall that South Carolina ran into some resistance when it tried to secede from the United States.

London's relaxed attitude is, ultimately, why Scotland is unlikely to break away. Two years ago, despite a question written by the SNP, a franchise altered to favor independence, a spike in the price of North Sea oil and a truly dismal pro-UK campaign, the secessionists couldn't carry the day. Nothing since then has strengthened their position.

Dan Hannan is a British Conservative MEP.