In the world that my grandparents knew and understood, Scotland, like the rest of Britain, was locked into a vast global trading bloc that preferred to haul frozen lamb and butter half way round the world from New Zealand than buy the same products from neighbouring France; that imported dried fruits from Australia rather than from the countries of the Mediterranean.

It was a trading system based on protective tariffs and trade barriers known as Imperial Preference. Britain chose to trade with the old “kith and kin” territories of the English-speaking world rather than with its European neighbours.

The Empire, the powerful, binding economic force of it, had, for generations, given Britons a common purpose, an enormous shared enterprise. It gave Scottish merchants access to trade with all the continents. The city of Glasgow, before its days as an industrial powerhouse, was built on trade - sugar and tobacco in particular.

Walk along the banks of the Clyde and the ghosts of that past are written into the place names: India Quay, Jamaica Street, Durban Avenue. Pacific Quay, where BBC Scotland now has its headquarters, was once Plantation Quay, a name that recalls a past that Scotland prefers to forget - its role in the trans-Atlantic slave trade.

But by 1974 the Empire was gone. Imperial Preference was gone. When Britain joined the European Economic Community in 1973, many of its old trading partners around the world - especially Australia and New Zealand - regarded it as a betrayal. The former British dominions and colonies had to seek new markets and new trading partners, as Britain turned its face away from them to embrace a new European identity.

The Empire became the Commonwealth, a community not of real economic might but of shared memory, of common values, of fellow feeling - in essence a community of sentiment, powerful sentiment maybe, but of sentiment nonetheless.

Did my grandparents’ generation feel diminished by this loss of stature in the world? Yes, I think they did, even personally so. The US Secretary of State Dean Acheson famously said Britain “had lost an empire and had yet to find a role”.

In the 1970s, politics seemed preoccupied with the management of national decline. In my first year as an undergraduate at Edinburgh University, as the Winter of Discontent took hold, we debated in our politics class, whether Britain had become “ungovernable”.

It was in that context that the SNP emerged as a new force in electoral politics.

If the glue of British union for my grandparents had been the common enterprise of empire, for my parents, born in the 1930s, it was no less strong. They came of age as the Empire was dying, but they lived as children through World War Two and the shared effort, and shared risks, of total war.

In the summer of 1940, at the start of the Battle of Britain, Winston Churchill told the UK it would have to “stand alone” in the breach. Other European countries were falling to the Nazis, compromising with them, or anxiously keeping their distance by declaring neutrality.

In 1945, Britain emerged from the conflict with a moral stature unequalled across the continent. This, too, that generation shared, and Britain continues to celebrate it, in ritualised memory and in popular culture, 70 years on - in Scotland as enthusiastically as anywhere else in the UK.

That generation was also bound together by what came after the war. The welfare state that the Attlee government built was another great shared British enterprise. The NHS, state pensions, child benefits, free education, increased social mobility - this was the Britain my parents inherited as young adults and it, like the Empire before it, had been a truly British enterprise.

And this is the world into which my generation was born and in which we grew into early adulthood.