Classic film noir is always set on American soil..
And I deliberately made a stupid and erroneous statement to get your attention. LOL
Honestly though, of the well-known films noir, I do think this film set in London is a marked exception. There are Hammer films made in the classic noir period, but they are only now being brought to the notice of modern audences.
The point I'm making is that this is true noir, but many movies labelled noir that take place otside the U.S. simply are not noir. Casablanca and Macao are two examples of films called noir for no reason other than the fact that they star actors who are noir icons. But the actor alone does not make the film noir, not even Bogie or Mitchum. And even notable French films of the 40's and 50's, IMHO, miss being true noir but belong more to other film styles.
Be that as it may, this movie is absolutely pure film noir and is one of few such from the classic era which is set in London or anyplace outside of the U.S. Nowadays, of course, every counry is producing notable neo-noir, but that's a different story.
Where am I from, you ask? "Pomona, Glendale, ((Fullerton, La Habra, Anaheim)), whatever."