Story Borrowed from Our Man in Havana?

I just watched Our Man in Havana last night. It's the same story line, right down to the overweight best friend who gets killed halfway through. A local businessman, in this case a vacuum cleaner salesman (played by Alec Guiness), gets recruited as a spy by a British agent. He desperately needs the money, so he begins feeding his control fantastic stories. The control gets all excited and passes the stories up the line, eventually to the prime minister. Oh what a tangled web ensues. By the time it becomes clear that the stories were fabrications, all the gullible higher-ups have to save face by pretending they were true.

I'm a great fan of John le Carre, although I never read The Tailor of Panama. It's hard to believe he would "borrow" so heavily from someone else's story line. With his experience, he has plenty of his own stories to tell. What's going on here? Does anyone have any ideas?