Devolution will put Scotland on a motorway to independence with no exits." This warning was delivered by Tam Dalyell (then Labour MP for Linlithgow) during the referendum campaign of 1997. Not everyone agreed with him, though Alex Salmond, the leader of the Scottish National Party (SNP), certainly did. That was why he campaigned alongside Labour's Secretary of State for Scotland, Donald Dewar. Devolution in his view would serve as a stepping — stone to independence. There were doubters in the SNP, the so-called fundamentalists who saw the offer of devolution as a Labour trap, but Salmond overrode their objections. Yet they had good reason to be sceptical. Labour's devolution proposals were unionist in intention, designed to check the nationalists. The White Paper, Scotland's Parliament, offered devolution to make for "the better governance of Scotland and the United Kingdom".

So we had the bizarre sight of the leaders of the SNP and Scottish Labour campaigning side by side to persuade us to vote for a constitutional reform which one intended should lead to the dissolution of the Union, while the other insisted it would renew and strengthen it. As I wrote, unavailingly, in too many articles at the time, "they can't both be right."

Comparable intellectual uncertainties and confusions were not new. As Colin Kidd shows in his new book Union and Unionisms: Political Thought in Scotland 1500-2000 (Cambridge University Press), they were evident 300 years ago in the debates on the Treaty of Union. Subsequently, from the mid-18th century to the last 30 years of the 20th, the Union itself was scarcely questioned. Kidd, Professor of Modern History at the University of Glasgow and a Fellow of All Souls, calls this "banal unionism" — the Union as a fact of life. Yet this did not preclude argument about the nature of the Union and its significance. That argument, never quite still in Scotland, rarely surfaced south of the Border, where the United Kingdom was generally seen as a Greater England. Nelson's famous signal at Trafalgar makes the point. There were Scotsmen, Irishmen and Welshmen in his fleet, but: "England expects every man to do his duty."