The seeds were sown in 1978 when the SNP and Welsh Nats blackmailed Jim Callaghan and his minority Labour government to hold a referendum on devolution. Those in favour couldn't muster 40% of registered voters in Scotland, so it fell by the wayside. Devolution was clearly rejected in Wales. The SNP's representation collapsed in the May 1979 UK General Election, but the idea of home rule for Scotland was there.
If the Labour Gov't ('74-'79) had given two fingers to the petit tribalists of the British Isles (including trying to please both Ulster Unionist and SDLP MPs at the same time) and gone to the country in 1978, they would have won with a workable majority. We all know what happened next. Perhaps the decline of the post war UK political, economic and social order, and specifically of subsidised Scottish steel mills and coal mines, was inevitable, and would have fed deep frustrations north of the border. However the personality and ideology of Margaret Thatcher, and limited Scottish support for the Conservatives under her, helped bolster the SNP. Then comes wise Mr Blair and devolution for Scotland and Wales, arrogantly thinking that a semi- federal arrangement eternally steered by Labour politicians on the ground, buoyed by grateful celtic clients, would keep the UK settlement intact.
In 24 hours a bunch of kids and some older political illiterates will probably break up the UK state. A tribal war has been successfully waged, as if Westminster was the headquarters of the English Colonial Administration. Westminster is so loathed - by all quarters of the UK - that the fact that its MPs were elected by us, including Scottish residents, seems somehow to not be understood. A "democratic deficit" is one of Salmond's rallying cries, yet every UK subject determines who forms the UK Government. Unless they can't be arsed.
The trouble is that if there is a narrow "No" vote tomorrow then a belated attempt to fire up enthusiasm for the political process in all parts of the UK will see devolution across its countries and regions. Scotland's nationalists may not be satisfied. The English rejected regional governments in the late 1990s (except in London). If they're offered their own national parliament then they will probably secede from the Union themselves, after the UK (possibly minus Scottish votes) comes out of the EU in 2017. We're doomed...