… in the abstract and also not literally in the concrete
It’s a delusion of a certain type of policy wonk that if you just tweak a society’s political institutions enough you will get the right outcome. A common reference point is the refoundation of West Germany after the second world war as an economic powerhouse with few external political ambitions (polite euphemism). That turned out no to be true. German political ambitions have been sublimated nicely into the EU where everyone can get on with pretending they do not exist. No harm there.
Can you parachute the Federal Republic into the UK and get the same outcomes? That is the hope of policy nerds. But no. Because there are no such things as political institutions. What we call political institutions are names for specific configurations of power, economy and culture. None is reproducible. Hitler did not come to power because the Weimar republic was not properly workshopped, but because it was politically brittle and unsupported by the political culture. They are not transferable between contexts.
The focus on institutions flatters us as policy nerds because it privileges us above all others. Yes, the globalists may exclude us from their clique at play time, and the populists may have taken our lunch money. But deep down we are biding our time., waiting for our opportunity to carefully balance powers between executive and legislative, and formulate the precise limits of judicial interpretation. We make a category error, just as recently when the UK media declared that British universities were ‘closed’, because the buildings were closed. Universities are not their buildings, and polities are not their texts.
That is why it is wrong to say that Britain uniquely has an unwritten constitution. All countries have an unwritten constitution. As the USA discovered recently, the ‘written’ part means nothing without the willingness of policy folk to follow the vastly greater set of unwritten and sometimes unspoken norms and conventions. The appearance of a working constitution just depends on periods in history when nobody tried to rock the boat, so allowing everyone to continue in their shared delusion that order is produced. That is how institutions function all of the time. The University of Edinburgh is a collective agreement about what we are. Writing it in stone and brick is very reassuring, especially when it comes time to put a pretty photo on the prospectus. And collective agreements can change.