I agree it would probably have to have been as drastic as that - though if Canterbury fell, just 60 miles from London...

I was put in mind of the Japanese attacks on Darwin in Australia, before the battles of Midway and Coral Sea put paid to fears of an invasion. We Australians like to think of ourselves as do or die types, but after the second bombing of Darwin...

"RAAF wing commander Sturt Griffith summoned his senior administrative officer, Squadron Leader Swan, and gave a verbal order that all airmen were to move half a mile down the main road and then half a mile inland. At this vague rendezvous point ... arrangements would be made to feed them. The order led to utter chaos. In being passed by word of mouth from one section to another, sometimes with officers present and sometimes not, it became garbled to the extent it was unrecognisable against the original. In its ultimate form it was interpreted, especially by those desiring such an interpretation, of an impending order for immediate and general evacuation of the area. Highly exaggerated rumours of an impending Japanese invasion had already reached the base from the town and spread quickly among those wanting to believe them. In the absence of restraint, men gathered their belongings" and abandoned their stations."

More than half the city of Darwin fled south.

I do still wonder whether Brits might have been similarly panicked by the news of Panzers in Canterbury...