When the fisherman gets out of his boat, he places the oars inside the boat. When Peter O'Toole gets into the boat the oars are in the oarlocks and ready for rowing.
While crafting his 'device' towards the end of the movie, the protagonist's hands are shown with full fingernails; contrary to one of the plot devices.
As Hunter tries to escape from his pursuers, he sees a sign pointing to the District Line. The District Line has never passed through Holborn Station - nor Aldwych, its stand-in for this movie.