Most of us tend to assume it's part of the timeless tradition? No, it's just a Nazi relic, says Mary Beard:
Hardly any commentator stops to mention that this silly torch ceremony has nothing to do with the ancient Greeks, and was really invented to be a magnificent shot in Leni Riefenstahl’s movie (choreographed by Carl Diem). This is one of Hitler’s most pervasive legacies.
Incidentally, if you're a connoisseur of Heathrow stories, Beard also has an eyewitness account of the chaos down west London way.