Their natural xenophonia and sense of superiority, and the British Empire all aside, I think the main argument for Britain not being part of Europe is a physical and hard-to-argue one: they're an island, as has been mentioned. You can, if you so wish, take a train, drive or even should you have the time and energy, walk from any country in Europe to any other. Try that starting from England and your car better be amphibious, or you better be wearing a snorkel!
