David Cameron's proposal for a referendum on Scottish independence might have caught opponents as well as allies by surprise. At first sight, the British Prime Minister seems to be setting the terms for the play on this issue. He appears to be outmanoeuvring Scotland's First Minister, Alex Salmond, by offering him what he wants, but with conditions; Mr. Salmond's Scottish National Party (SNP), which holds an absolute majority with 69 of the 129 seats in Scottish Parliament, is committed to a referendum on independence. The catch is that the outcome will be binding provided the U.K. parliament at Westminster and the devolved regional chamber at Holyrood in Edinburgh agree to it and provided the plebiscite occurs within the next 18 months. If held after that, the result would be only advisory. It also suits Mr. Cameron that Scottish public opinion is currently running at 32 per cent for independence; there is more support in Scotland for stronger devolved powers within the U.K. In addition, the 18-month deadline would enable a binding referendum to be held a year before the iconic 700th anniversary of the battle of Bannockburn, in which a Scottish army defeated a larger English one. Furthermore, Mr. Salmond cannot reject a referendum and is trying to influence the argument by insisting on a date late in 2014.

But Mr. Cameron's gambit is also high-risk. As he has not consulted the other pro-union parties, in particular Labour and the Liberal Democrats, it is unclear if he aims to preserve the union or merely score party-political points against the SNP. The majority of Scottish voters have backed the centre-left since the mid-1980s. Mr. Salmond has drawn on widespread resentment of Westminster dominance without slipping into ethno-nationalism; for example, SNP Members of the Scottish Parliament have taken their oath of office in Urdu, Italian, Gaelic, and English. Mr. Cameron might have played into the SNP's hands by provoking Scots to accuse him of interfering in their nation's affairs; they are also angry about his choice of Lord Forsyth, a former Cabinet Minister for Scotland who is very unpopular north of the border, to put the argument for a referendum. Constitutionally, only Westminster can legislate for Scottish independence, but it remains the case that no British parliament can bind its successor. That in turn means that even if the Prime Minister forestalls Scottish independence now, he could well generate enough opposition in Scotland to ensure the dissolution of the United Kingdom in the not inconceivable future. Ironically, Mr. Cameron leads what used to call itself the Conservative and Unionist Party.

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