The flag of the United Kingdom (from 1801) and the flag of the United States of America (from 1960).
The British flag used here has a 1:2 ratio and the American flag a 19:20 ratio, resulting in the US flag being somewhat shorter than the Union flag when both flags have the same width, as here. (Use of this image or either flag in it in connection with either Britain before 1801 or America before 1960 would be anachronistic.)
This file was derived from:

 Flag of the United Kingdom.svg
Flag of the United States.svg
Own work based on: Flag of the United Kingdom.svg  and Flag of the United States.svg