The referendum on Scottish independence, due on 18 September, comes at a time of growing opposition in the UK to remaining in the EU. This is significant because Scotland is the strongest base of pro-European sentiment in the UK.

A poll conducted earlier this year determined that if a referendum on continued EU membership had been held in June in the UK as a whole, 47.1% would have voted to leave, with 39.4% voting to remain. But a poll in February 2014 showed that in Scotland, 48.7% would vote for the UK to remain in the EU, with 35.4% voting to leave. Of course, it is premature to draw any firm conclusions from these figures.

The referendum on exiting the EU that David Cameron has proposed may not take place, regardless of the success (whatever that may mean) of his promised “renegotiation” of the terms of British membership. But as a result of various ostensibly minor issues, the likelihood of a British exit seems to be increasing – which fundamentally alters the importance of the vote in Scotland.

For example, the appointment of the relatively unknown Jonathan Hill, the leader of the House of Lords, as the British member of the new European commission headed by Jean-Claude Juncker is just the latest in a long series of British EU errors. Cameron’s spokesman said in July that at his first meeting with the new commission president Cameron would seek a prestigious portfolio, such as the internal market, for Hill. Juncker’s office coldly replied that important portfolios in the new commission would go to major political figures, and that Juncker “does not owe [Cameron] anything”.

Given Cameron’s opposition to Juncker’s candidacy for commission presidency, the abuse to which Juncker has been subjected by the British press, and Hill’s lack of centrality within British politics, Cameron may be justifiably nervous when Juncker announces his appointments to the new commission. Juncker, after all, has many senior politicians to accommodate, and their approval by the European parliament is no minor matter. And, though it was perhaps unsurprising that Cameron should be unenthusiastic about Juncker’s candidacy, the vehemence of his opposition was extraordinary. Cameron no doubt wished to reassure those in his party who doubt his eurosceptic zeal. Even so, his supposed remark that the UK was more likely to leave the EU if Juncker’s candidacy succeeded was strange and disquieting, not least because any renegotiation of the terms of British membership will be carried out primarily with other member states, not with the commission.

Cameron’s bid to thwart Juncker’s candidacy mirrored his unsuccessful attempt to prevent the adoption of the EU’s fiscal compact in 2012. He overestimated German chancellor Angela Merkel’s willingness and ability to support the British position. Many influential Germans are reluctant to help Cameron in what they regard as his self-created European problem. They will not allow Merkel much latitude here, even if she seeks it.

If Cameron’s advisers overestimated the support they might have received from Merkel and others, they clearly underestimated the power and effectiveness of the European parliament. For many months it had made it clear that it had specific ideas about how it would exercise its new powers, granted by the Treaty of Lisbon, over the commission presidency. But the rapid post-election agreement among the parliament’s major political groups to support Juncker caught Cameron off guard.

Far from enhancing British influence, threats of withdrawal have undermined the UK government’s credibility within the EU, as colleagues have become disinclined to engage in significant compromises with a UK that may not be a member in two years. Traditionally, EU heads of state and governments try to help one another with their domestic political problems. But there is a growing sense in the European council that Cameron is abusing this goodwill.

Thus, Cameron’s claim that Juncker’s election would make it more difficult to ensure the UK’s continued EU membership risks becoming a self-fulfilling prophecy. To present Juncker’s candidacy as a matter of high political principle, with Cameron heroically but unsuccessfully standing alone against the dark forces of federalism and centralisation, could have only reinforced English feelings of alienation from Europe. That is less likely to be the case in Scotland.

If Cameron returns as prime minister after the general electionin 2015, he will face an uphill battle in renegotiating the terms of British EU membership owing to resistance not only from his European partners, but also from his own party, which is close to advocating British withdrawal. Indeed, it is difficult to see how a re-elected Cameron could maintain the Conservatives’ unity without endorsing a no vote in the referendum on the outcome of his own renegotiation.

Britain’s EU membership will be one of the major issues at stake in next year’s election. It would be a tragedy if British voters cast their ballots without fully understanding the European implications of their choice. One thing, however, seems certain: if Scotland votes for independence in September, a referendum within the rump UK on continued EU membership would be even less likely to produce a victory for those who wish to remain.

Copyright: Project Syndicate