Exactly. I live just outside London, and the big class system is obvious. Most people are in the 3rd tier the OP mentioned, i.e. lower or working class. Most people I know and work with are in the middle class. And there is the unreachable upper class that owns most companies and land. You generally have no connection to them.

But I grew up and lived in several other Northern European countries where there is mostly just a huge middle class. Sure, some differences between upper-middle and lower-middle. But not a lot, and they can live side by side, go to the same school etc.

There are the odd billionaires, big estate heirs and royals i.e. classic upper-class but very few and they don't own everything. And they might also live near you, their kids might go to your normal public school etc. And then there are some unfortunate that could be classed as in a lower class but that is very few, and not everywhere, mostly just in the big cities. Mostly recent immigrants that do the jobs no-one else wants to do. They quickly get swallowed up by the middle class once settled.

Unless I was very sheltered that seems to be the case for most countries in Northern Europe apart from the UK?

Id say you’re righty as far as “Northern Europe” being Scandinavia+Germany. The Uk but london specifically is actually a pretty decent example of a contemporary protodystopia (I live there). On one side you have Mayfair which is like Monaco with some of the richest people in the world living there(and often the most corrupt - Russians, Saudis, Chinese oligarchs, African dictator’s families) side by side with Tower Hamlets in East London where a substantial amount of children suffer from malnutrition.

Malnutrition! And Tower Hamlets is of course a 5 min walk to the very core of the City of London.