Close. Linked by CasuallyObservant is the "Royal Standard of the United Kingdom".
In the picture is the "Royal Standard of the United Kingdom for use in Scotland"
It is very similar, but quadrant arrangement and content is slightly varied.
Not enough of an issue to address - unless one is being quite particular regarding official royal protocol ...
It is wrinkle.
What kind of artwork on that flag? Those are very strange.
Looks like the "coat of arms" for the royal house of the Kingdom of Great Britain.
Don't think so.
"Coat of Arms" for Kingdom of Great Britain on Wikipedia https://en.wikipedia.org/wiki/Royal_coat_of_arms_of_the_United_Kingdom
Even the colors are wrong.
This is exactly what it is:
https://en.wikipedia.org/wiki/Royal_coat_of_arms_of_the_United_Kingdom#/media/File:Royal_Standard_of_the_United_Kingdom.svg
Close. Linked by CasuallyObservant is the "Royal Standard of the United Kingdom".
In the picture is the "Royal Standard of the United Kingdom for use in Scotland" It is very similar, but quadrant arrangement and content is slightly varied.
Not enough of an issue to address - unless one is being quite particular regarding official royal protocol ...
Good find to CasuallyObservant.