Churchill was asked what the Government's plan was in the event of a German invasion, where would they go if the defense was unsuccessful? He said there was no plan, that the War Cabinet had never even discussed a plan.
BTW, I highly recommend Darkest Hour. There is a fair amount of Hollywood exaggeration if not fiction, but it's a damn fine movie. Gary Oldman should be a unanimous pick for Best Actor.
It'll be interesting to see more reactions to the movie, as you probably recall, Gary Oldman got in hot water a few years back for some comment he made about Jews in showbiz.