As I recall, the people interviewed in Michael Caine's film who couldn't remember the Battle of Britain were Americans outside the US Embassy in Grosvenor Square. One man recalled it very well and greatly appreciated what the UK was up against.
The Battle of Britain is less than a lifetime ago, several of those who fought it still survive and those events still live in - and perhaps effect - the memories of probably several million people and their children like me. We don't celebrate it, we commemorate it. In a hundred years it probably will just be paragraph or two in a dusty history book.