I stick to the view I have always held that Hitler missed the bus in September 1938. He could have dealt France and ourselves a terrible, perhaps a mortal, blow then. The opportunity will not recur.
Letter to Hilda Chamberlain (30 December 1939), quoted in Maurice Cowling, The Impact of Hitler. British Politics and British Policy. 1933-1940 (Cambridge: Cambridge University Press, 1975), p. 355.