Supporters of the campaign for Scottish independence have taken a beating in recent weeks. First, Mark Carney, the governor of the Bank of England, came out with some disparaging sentiments about the consequences of Scotland leaving the UK. Carney is Canadian and has no political or sentimental ax to grind with regard to independence—this is hard-nosed economics. Then, the Scottish financial industry, which accounts for 9 percent of Scotland’s economy, delivered a similarly disapproving opinion.

With a referendum on Scottish independence set for September 18, many big guns from business and industry, together with all the UK’s main political parties, are lining up to warn how damaging a separation would be for the Scottish people. British Prime Minister David Cameron will give a major speech in London today warning against Scottish Independence.

Indeed, a Yes vote would have enormous consequences for the UK and for Europe. The break-up of Britain would require a period of adjustment for the remainder of the UK, but it would also have huge ramifications for the EU.

The leader of the Scottish National Party, Alex Salmond, who is driving the campaign for independence, has found himself in a bit of a pickle after proposing that Scotland could leave the union with England after three hundred years but maintain the pound sterling as its currency. With the infelicitous example of the euro fresh in everyone’s memories, few people think much of the idea of a common currency for separate states.

Salmond’s biggest problem, however, is that polls have shown consistent popular opposition to independence for the past year or so. According to one recent survey, 52 percent of the Scottish electorate want to stay in the union, and only 32 percent want to leave; 16 percent are undecided. Salmond has just over seven months to turn that around before the plebiscite, in which only those registered to vote in Scotland can cast their ballots. Residents of the rest of the UK have no say.

For the UK to lose 10 percent of its economy, which is what Scottish independence would mean, would make the government in London look weak and disorganized. Yet there is a serious lobby in the ruling Conservative Party that tacitly supports independence. They argue (although only in private) that because the opposition Labour Party has 41 out of Scotland’s 58 members of parliament in the House of Commons—seats that would all disappear if Scotland were to secede—a vote for independence would have a negative impact for Labour and so give the Conservatives a political advantage.

But Conservative leader David Cameron knows that it would be hard to recover from being the British prime minister who presided over the end of the union.

At the same time, he wants to keep Britain in the EU—especially as the Germans, Americans, and much of big business are urging him to do so—while having to wage a Euroskeptic campaign to dampen the impact of the rightist, anti-EU UK Independence Party (UKIP).

UKIP, under its leader Nigel Farage, is expected to score significant successes in the European Parliament elections on May 22–25. That contest may effectively be the first round of the Scottish referendum, because a big vote for UKIP would give the pro-independence campaign in Scotland a tremendous boost.

Scots’ greatest fear is that the UK may leave the EU, and if Scotland were still part of the UK, Scotland would be forced to leave too. So the greater the vote for UKIP, and the higher the risk of the UK quitting the EU, the bigger the vote for Scottish independence. At the European Parliament elections, Britain’s established parties are fighting for more than just saving face—they might be battling for Britain’s very existence.

Yet even if Scotland were to become independent, the EU would have to decide whether to allow Scotland to obtain membership without applying for it. The Catalans and those in other parts of Europe with separatist ambitions will be watching that decision like hawks, ready to swoop with their own demands for independence.

There is, of course, no precedent for an existing EU member state splitting up. As much as the EU likes to insist that it is based on rules and principles, the status of an independent Scotland is the type of big question that will be decided by political expediency above all else.