The Union Flag was originally a Royal flag. When the present design was made official in 1801, it was ordered to be flown on all the King’s forts and castles, but not elsewhere.
As @[email protected] said:
Also interesting to note is that the red diagonals aren’t centred within the white, which means it’s possible (and surprisingly common) for people to fly it upside down by accident.
That’s not the Irish flag
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https://en.wikipedia.org/wiki/Saint_Patrick's_Saltire
It has a long history in Ireland.
It represents Ireland nonetheless (well, now it represents Northern Ireland, but still).
As does the Confederate Flag for the US…does not make it a recognised flag of Ireland.
To quote the first paragraph of your link
"Most Irish nationalists and others reject its use to represent Ireland as a “British invention”[2] “for a people who had never used it”.
We had our own flag previous to this and after it, before we settled on what we have today.
Rule of thumb, the Irish decide what represents the Irish not the UK establishment.