Congratulations on reaching your century Daddycool,
Ken's comments about the flag got me curious so, being nosey, I have done a little investigating. Wikipedia states:
"Whether to use "Union Flag" or "Union Jack" is a matter of debate. One view is that "Union Jack" should be used only for the flag when it is flown as a jack (a small flag flown at the bow of a ship), but it is not universally accepted that the "Jack" of "Union Jack" is a reference to such a jack flag and is only an educated guess............"
So I guess either Union Flag or Union Jack is OK.
Further it shows that the 'Ensign' (whether Red, Blue, White or Green) is the flag flown at the stern of a ship.
However the Union Flag/Jack is most certainly British and not English so I would claim poetic licence on that one Daddycool. 
Nice song and it is good to promote a bit of discussion.
Roger