Roberts, Andrew. "Hitler's England: What if Germany had invaded Britain in May 1940?"
Divergence: 1940 CE
Summary: Discusses the reasons why a British invasion did not occur, but then looks into what might have happened if Germany had been prepared to invade in the late spring of 1940. Topics include the susceptibility of the British populace to collaboration, who would have headed a puppet goverment, the likelihood of counter-invasion, etc.
Published: In Virtual History: Alternatives and Counterfactuals (ed. Niall Ferguson), q.v.