When Trout and Waverley stop their car in the desert to consult a map, Waverley points left and states that Cairo lies in that direction, then points right and says that the Red Sea is in that direction. Cairo is west of the Red Sea, so logically he's just pointed west, then east. Waverley then looks forward and tells Trout that England lies that way. They are actually looking south, with their backs to the correct direction.