What would a standalone Britain look like? We don’t really know because there has never been one. For its entire history, Great Britain has been part of something bigger. By the time King James united England and Scotland under one crown the imperial project was already under way. By the time the two countries were formally united, England had a sizeable empire. Scotland had tried to build a rival empire and its failure forced it into unification with England. Great Britain was a product of empire.
It wasn’t plucky little Britain that stood alone against Hitler in 1940, it was a global superstate called the British Empire. It was a global superstate on its last legs but it was still able to marshal enough resources and manpower to keep the Nazi state at bay until America and Russia joined the war.
Then, almost as soon as that empire was dismantled, Britain joined another larger entity, the EU.
So to find a standalone Britain you have to go back much further. As Fintan O’Toole says, you have to go back to that period after the kings of England had lost their territories in France and before the union of crowns in 1603; in other words to Tudor England. A post-Brexit Britain is very likely to resemble the Tudor realm territorially. If Scotland quits the union, we are left with England, Wales and a sliver of Ireland, not that different from the England of Henry VIII. Instead of going back to the 1950s, it will be back to the 1550s.
We tend to think of Tudor England as a golden age when the country was on the rise. It is true that, towards the end of Elizabeth’s reign, England enjoyed some military successes. For most of the period, though, England was weak, walking a diplomatic line between France and the Hapsburg domains. But Tudor England was a weak country growing stronger whereas post-Brexit Britain will be a strong(ish) country growing weaker. It is true, as the Leave campaigners say, that a post-Brexit Britain will still be a large economy with significant military and political clout but it will still be much diminished. For historians, this will give Britain’s history a pleasing symmetry. As it saunters off the world stage, the country will assume a similar shape to that which it had when it burst onto the world stage 400 years earlier.