It was the flag of the British Empire with all that entails. It is to be found all over the loyalist areas of Northern Ireland and on Orange Marches. It has appeared in umpteen far right demos, and in fact if you look at 1970s far right footage you can see it is the flag they most commonly carry in the UK not the St. George's Cross.

Oh, and you'll find it at plenty of football matches, notably Glasgow Rangers, who fly it while singing songs about wanting to be "up to our knees in Fenian blood".