Christmas decorations go up in Britain even earlier than they do in the U.S. and by early November most of Mayfair, Marylebone and Chelsea are awash in Christmas lights and ribbons. Even though many London residents aren’t Christian, the whole city seems to revel in the holiday festivities. One theory is that in the post-Brexit United Kingdom, holiday traditions like Christmas trees and Boxing Day are more unifying than patriotism, so the whole country joins in the cheer. In fact, there may be n...