The Americans have 1776, the French have 1789 and we have 1940. The date is not official for us the way it is for them; it marks no formal founding of a nation or republic. But the events of that year — specifically, Britain’s lonely stand against the Nazi menace — have acquired the status of a creation myth, the heroic and finest hour in which modern Britain was born.Our children study the second world war in school and when we vote for our Greatest Briton we choose the hero of 1940, Winston Churchill. When David Cameron deployed his quasi-veto in Brussels in December, the headline-writers and cartoonists instantly reached for 1940 and the image of the solitary Tommy: ‘Very well, alone.’ Meanwhile, an unlikely Twitter sensation, with more than 200,000 followers, is RealTimeWWII, providing 140-character updates of what happened on this day and at this hour in 1940.