I remember seeing this in a movie theatre in the 60s and was stunned. Now I watch it regularly on dvd. Arguably the greatest spy film from the greatest spy novel.
It's hard for anyone to beat Le Carre when it comes to Spy novels as you say David and the movie is highly underrated especially as in my opinion it has a strong Noirish element.
Len Deighton comes the closest, I think, Funeral in Berlin and Horse Under Water in particular, but with the Berlin Game series in the 80s. I agree, The Spy Who movie is very noirish, the b&w photography just stunning, and Burton the perfect doomed protaganist who gets the double shuffle from his own side. No femme fatale really. But then few films noir actually had one.
I need to make time to read the Deighton books. Funeral in B and other movies like Quiller Memorandum have always held an appeal for me. You're certainly right above the absence of a Femme Fatale in many types of Noir movie as it can take many other forms.
Quiller is a good one I watched time and again. Kremlin Letter is good as well.