It’s all about geography.
For most of their history, the states located on the British Isles have been peripheral and on the margins of their civilisation, that is to say Europe. To an extent, this has also reduced their exposure to that civilisation’s wars and allowed their societies and institutions to develop in more continuity than, say, Poland’s. This has bred a sense of exceptionalism and insularity.
For a brief period, as our civilisation perfected maritime travel, our peripheral states flourished as we exploited our geography to enrich ourselves. For a couple of centuries, this put us at the heart of our civilisation as opposed to its periphery. This brief period in our history is over, but many of us haven’t grasped that yet because it is still within living memory, just. This further feeds our sense of exceptionalism.
But the reality is that we are just another collection of European states, nothing special except insofar as that in itself is special. We are back at the periphery, and actively doing all we can to exaggerate our peripheral nature, isolating ourselves from the mainstream of our civilisation, limiting our influence and interest, turning in upon ourselves.
Geography can’t be changed. We were lucky in the 17th, 18th, and 19th centuries. But this is the 21st and we’re back to where we’ve been for all the other centuries – out on a limb.