It all came down to the Battle of Britain. After Dunkerque it would take months to reequip the Army and train enough new soldiers to be able to defeat the Germans on land. But, the Germans could not get an invasion force past the Royal Navy - unless they could establish air superiority over the Channel. When the Luftwaffe could not defeat the Royal Air Force, Hitler knew the jig was up and abandoned invasion plans.
What an astounding leader. He reminds me very much of our current president. In the beginning, no one took him seriously. In the end, his leadership kept England alive and free until the US entered the war. The sad part is that within 2 weeks of VE day, he was voted out of office because he hated socialism.
So far as I know, however, there was never any actual planning.
https://en.wikipedia.org/wiki/Operation_Fish