American here, relatively well-read. My sense is that post-1945 Britain took a sharp turn - from "let's all work together for the common good" to "let's pretend that our country has a decent future...while quietly looting its not-dead-yet body for our own individual benefit".

Well, not quite that simplistic. And WWI was also pretty brutal for both Britain's situation and outlook.

IIR, Adam Smith was very clear about the differences between healthy, virtuous capitalism, and the evils of maximize-how-much-the-self-serving-rich-can-squeeze-out-of-the-little-people feudalism.

Not quite immediately post-45. That was when the modern welfare state was being put together. Winning a war was the peak of state capacity. Things were still going OK around 63 and the "white heat of technology" speech (why can I not easily find a full transcript of this?). Wheels came off in the inflation era leading to the "winter of discontent", followed by a massive and explicit backlash against socialism and in favor of individual profit. Thatcherism. North Sea oil solved the money problems, but papered over the more structural problems. Blairism managed a second financial services boom, but then .. 2008. And we've never recovered.