September 18, 2014 is a crucial date for the future of the United Kingdom. It is the first time that a vote will ever have been held with the consent of an entire national community on dissolving the terms of one of the UK's foundational political unions while that Union was still in effect. It is a mould-breaking challenge to the nature and continuation of the UK as a state actor.
On that day, Scotland will vote on whether to be an independent state. If that vote is carried, Scotland will have full state powers: a sovereign government, an international personality, independent armed forces.
While victory for the Yes campaign still looks unlikely, four recent polls suggest a Yes vote ranging from 41% to 46%. This is dangerous territory: should the vote end as a No, the Yes vote would have been high enough to mean that nothing can be quite the same again. And that is the impression you get living in Scotland: whatever the result, the genie is out of the bottle.
How on earth did we get here? As I argue in The Road To Independence? Scotland In The Balance, the roots of the current situation go back quite a long way. Scotland is still – though less than 20 years ago – routinely referred to as a 'region', a term that seems never to have been used of the country before the Second World War.
Legally and culturally, Scotland is a national entity in a British union: socially and politically, this is less certain. British values and society are still often seen as unproblematically unitary by commentators.
The Labour leader, Ed Miliband, has made much over the last two years of 'One Nation' values and policies: in reality, he must know that the UK is ruled by four governments comprising six political parties, two of which want to end the state.
For most of the period since 1707, Scotland was recognised as a subsidiary 'British' nation, in a world where it was equally possible to be British in Canada and New Zealand.
Until the 1940s, the double compact of Scotland's Union with England held. In Scotland, domestic society and its institutions were under Scottish control; in the British Empire, Scotland had national status and huge opportunities to place its educated groups in senior roles.
Even in regional grammar schools in Scotland, up to 40% of those whose obituaries appeared recently had imperial connections. Throughout the Empire, Scottish associational groups – Caledonian Societies, Burns Clubs – existed to help network Scots and ensure that they took jobs and social opportunities in the colonies ahead of their rivals from elsewhere in the British Isles.
Scots were part of the British family of nations: the Empire also gave Scotland, as a nation, access to world markets. Just as the often-unjust Empire vanished in the 1960s, so did the Union's preservation of a protected domestic public sphere as the counterpart to equality of imperial opportunity.
The creation of a unified British social and economic policy on an unprecedented scale after 1945, combined with the early stages of modern globalisation, undermined the bargain of domestic control within the Union as surely as withdrawal from empire undermined the imperial bargain.
The rise of the SNP in the late-1960s was, in many respects, a reflection of this state of affairs: a declining domestic economy and the loss of an international role.
'British values' have shifted radically over time; but the British state itself can be traced most consistently not through these, but the sequence of unions through which it has evolved as a constitutional entity.
To demonstrate this one has only to notice how the unionist case for Irish integration altered from the politically central concerns of the British elite in 1900 to an issue which they addressed over the heads of Northern Irish politicians by 1985.
In the latter year, the Anglo-Irish Agreement demonstrated that even a Right-wing Conservative government saw the future as Westminster-Dublin co-operation irrespective of the views of Northern Ireland's unionists, who were 75% opposed to the Agreement.
Irish participation in Britishness was written out of British history after Irish independence, to the extent that a study such as Linda Colley's Britons (1992) could leave Ireland out altogether: conveniently, since the patriot Parliament of 1782 and many aspects of the Volunteer and United Irish movements directly contradicted her underlying thesis that Protestantism promoted British integration.
The narrowing lead for the No campaign in the polls has perhaps led to David Cameron's intervention in a debate which he has long claimed was Scotland's decision alone. Will his entry into the debate be more effective than the attempt to unite the UUP with the Conservatives in the 2010 election?
In the event of a Yes vote in Scotland, Sinn Fein would surely push much harder on a 2016 all-Ireland referendum, which might be difficult to resist. Threats of dissident republican violence in the event of a Yes vote emanating from some in the arch-unionist camp would show to be without substance.
Scotland's vote would endorse the value of a civic and inclusive nationalism (Rowntree Trust research shows that the vast majority of BME Scots identify as Scots) and would undermine the claims of ancient ties of blood to some imagined Scottish nation of genetics, not politics.
A Yes vote would herald a commitment to a modern, democratic Scotland at odds with the militarist and tribalist elements of its history, and this would have a knock-on effect on the sustainability of ethno-cultural Northern Irish Unionism. Progress would, however, probably be slow.
The vote of September 18 could change not only Scotland, but the whole UK.