for Colin B - a short history lesson
Henry VIII was King of England long before the Union of the Crowns and the subsequent Act of Union (of the Scottish and English Parliaments) which established the United Kingdom of Great Britain and Northern Ireland. You share the same misconception as many other Englishmen that the UK equals England. It does not and Elizabeth Windsor is Queen of the United Kingdom of Great Britain and Northern Ireland. SHE IS NOT QUEEN OF ENGLAND quite simply because there is no Kingdom of England and therefore no such role. Equally there is no established religion in the United Kingdom, in which respect England and Scotland maintain their quite separate religious establishments.
You are however right in that everyone joining the UK Armed Forces takes an oath of allegiance to the monarch as commander in chief (as I did when I was commissioned into the RAF many years ago) but that is quite different to an oath of allegiance to any religion.