Are you being, and l choose this phrase very carefully, deliberately obtuse?
Britain is surrounded by water. It's therefore impossible for Nazi Germany to roll in the tanks and march in the troops. British people who wanted to enlist in the fight against fascism did so and of course there was conscription back then, others remained to aid the war effort at home as Britain could only be attacked by air. There is no equivalence here as for Brits in WW2 it wasn't a choice between fleeing or fighting an enemy who had literally invaded however, even so, it's not for any of us to assess the characters of people seeking refuge from war and it's actually quite unpleasant to see armchair military strategists on this website with a hard on for war speaking in condemnatory terms, from a very safe distance, about the civilians within shooting distance who choose to flee.