So, I take it that Battle of Britain Day, as noted below from Wikipedia, is not a holiday.
"The 15th of September, also known as Battle of Britain Day, is now an annual commemoration of the battle in the United Kingdom."
Looking at the list of holidays in the UK, it appears to be absent any recognition of soldiers who served and died in wars. I am surprised by this and, therefore, BBD gets my vote as a national holiday in the UK. In the US there is Memorial Day (end of May) and Veterans' Day (Nov 11).
Richard L.