What percentage of people left the cities in anticipation of such events? The narratives I've seen on the Japanese bombings was that people strategically moved to the smallest villages they could find family in.
For those that stayed behind there was a post-war pride that they stuck it through and didn't give in, but it must have been unimaginable even with the bomb shelters and London Underground. Again, this is what I've been taught from my elders so not first-hand experience.
EDIT: I should add that I realise it was not just Britain for whom things were unimaginable.
EDIT 2: Another factor that must have had a big effect on Londoners was that the king and queen stayed at Buckingham Palace (which was hit a few times) during the war.
I can't remember whether ration cards were location-restricted as well, or whether there were bureaucratic obstacles to freedom of movement.
As others have pointed out children were evacuated, but realistically a lot of people have jobs to do that they can't just do elsewhere and most people just don't believe things like that will happen to them and certainly not here (there is a TED talk by a photographer of the Bosnian war about this that I cannot find right).
Finally, this is British people we are talking about: a stiff upper lip is basically their national idea (or was).
Regardless I hope I would have the foresight to do some vamoosing of my own, in case things went that much south.
"At Home in America you were in a country at war. Now, however, you are in a war zone."