Invasion!: Operation Sea Lion, 1940 1e uitgave

It's the summer of 1940 and the Nazis have crossed the English Channel to invade Britain. They advance North from the South coast and great swathes of Southern England come under German control. Fiction, of course, but an invasion of Britain was planned by Hitler to take place in the summer of 1940 - how far would the Germans have been able to advance? Would they have been successful?