People sometimes ask, “Is London the capital of France?” No! That would be Paris. I once overheard a guy in a bar say, “I’m going to London, the capital of Europe.” His friend replied, “Mate, you’re going to a city, not a continent.” Everyone laughed, awkwardly.
Another classic: “London is the capital of Britain.” Well, “Britain” usually means Great Britain, so you’re close! But if you want to be pedantic (and let’s be honest, we all love being a little pedantic), say “Great Britain” or “the UK.” Your friends will either adore you or avoid you. Proceed with caution.