Margarita's song about Harlem and Dover was apparently used as a drinking game by Sussex sheep shearers, who wore hats made stiff and waterproof with tar. The idea was to hold the hat by the brim with a horn beaker of beer or cider (that's British alchohol-rich cider) balanced on the crown, and while everyone else sang the first part, the drinker (victim!) attempted to drink it dry in one swallow, and then, at "turn your glasses over," toss the beaker in the air, upturn the hat and catch the falling beaker in it. Though my father remembers his shepherd grandfather, that isn't where I found this, but we've a lot of books (including the Coppers) about Sussex shepherds, a fashionable subject in the thirties, and it could have been in any one. It did not give any more verses. As the penalty for failing the task was to repeat the attempt, more verses may have been lost in the mists of antiquity and alchohol.