Okay, to quote what websafe is talking about:

"Ancient sources, both written and visual, provide a consistent view of Socrates’ physical form. His appearance was often compared to that of a Silenos, with regard to his stocky, broad-shouldered body (Plat. Symp. 215a ff.; Xen. Symp. 5.7), thick neck (Cic. De Fato ch. 5), protruding belly (Xen. Symp. 2.19), baldness (Sidon. Apoll. Epist. 9.9.14; Lucian, Dialog. mortuorem 20, Menippi et Aeaci 417), prominent eyeballs (Xen. Symp. 5.7), broad nose with wide nostrils and large mouth with thick lips (Xen. Symp. 5.7)."

I do agree that in this case, 'Socratic' refers more to the guy's facial expression/attitude ("frowning on a younger world,") than his actual features.

That le Carré used facial definition as a means to convey the person's attitude, using this very specific adjective otherwise limited to qualify philosophy and not physical description, seemed intriguing to me.