On reflection, I discovered that the Union is good for three things. The first is the stronger security of political liberty. This year we celebrate the 800th anniversary of Magna Carta, when the English Church and barons compelled King John to accept certain limitations on royal power. Partly as a consequence of this, foreign observers in the late medieval period — not least in France — remarked on the extraordinary extent to which English monarchs were held accountable by parliament. And one reason that some Scots in the 16th and 17th centuries hoped for unification with England was that English law might come to constrain the arbitrary feudal powers of the Scottish nobility. After the Union of England and Scotland in 1707, the English and the Scots together — that is, the British — pursued a political path that led to increasing constraints upon royal power and increasingly accountable government. This path was not universal: many other countries didn’t follow it, and in the 19th and early 20th centuries Britain’s democratic model was widely admired by liberals throughout Europe. However, after the end of the Second World War in 1945 with the defeat of Nazism in Germany, and especially after the end of the Cold War in 1989 with the collapse of the Soviet Union, liberal democracy became more widespread, not least in Europe. As a consequence the political model that the British have pioneered came to appear less exceptional and more normal. As a Foreign Office official once put it to me, we British had become the victims of our own success.

Sometimes, however, appearances deceive, and they do so here. Recent developments in the world should remind us that the liberal democratic political system that we, the British, have played a leading part in developing is not a piece of the cosmic furniture. It’s not the natural, default position of human political life. It’s contingent and vulnerable and precious. It’s an important historical achievement, which cost our forebears much to build and defend, and which we could lose. In the light of Russia’s recent veering in an autocratic and aggressively nationalist direction, in the light of the rise of an increasingly belligerent China ruled by a Communist Party that is neither liberal nor democratic, and in the light of the atrociously inhumane politics of ISIS and other jihadist movements in Nigeria and Sudan, it should now be clearer to us that the political liberty, accountability and humanity that we have achieved in Britain should not to be taken for granted. They may not be unique in the world, but nor are they universal or secure.

Of course, if Scotland were to secede from the Union, it would most probably continue to maintain the liberal democratic political institutions and customs that the British had developed, notwithstanding the illiberal, cyber-intimidating, street-thuggish elements that certain reaches of Scottish nationalism have spawned or the habitual preference for centralised control that the Scottish government has exhibited. Nevertheless, there’s no doubt that a United Kingdom would be stronger both diplomatically and militarily, and so better able to secure liberal democracy, than would an independent Scotland and a British rump.