It’s been around since at least 2018, but I only discovered the BBC Sound Effects archive today. It hold clips of pretty much any situation you can think of, including city-specific soundscapes, like those from London.
I’d wager most the sounds Londoners most associate with the city are those of the Underground, but for me, it has to be the Invitation to the Jellicle Ball from Cats. Something about that just screams London.