First, the oldest operating mint in the world is the Royal Mint. While it is no longer located in the Tower of London, or even in England, it has become well respected due to its lengthy existence. The current location of the Royal Mint is in Wales.
One of the mainstays of the Royal Mint is the Gold Sovereign. This coin has been minted since 1817. The Royal Mint is much older, approximately one thousand years old.
During the days of the expansive British Empire the Royal Mint had branch mints in other countries. Thus, the Gold Sovereign has become quite popular in Australia.