During the Gascoigne era in particular, I'd see boys in a particular Fife school steadfastly supporting England. Mind you, some of them were also in a [very bad] Orange flute band. I hear what some people have said about Rangers supporters promoting the union rather than England, but at that time there were certain groups that saw the two as being synonymous. That included involvement in sectarian matters. It's not as bad as it was, but it's still there in certain circles.
I'll not derail much more, but I recall some extremely bizarre conversations with boys who proudly told me that being a Protestant meant that you didn't go to church. They had some really very confused ideas.
I was told by some retired miners in the area that the sectarian nonsense had been imported from the west of Scotland many years previously.
I note that above, someone commented that St George flags are used to represent England. That certainly should be the case, but at that time I recall that England supporters were flying union flags rather than the St George flags currently being used. (Rugby was an entirely different matter.)
I recall my dismay when some of the bigotry was briefly imported to Cowdenbeath football ground at the point when Rangers was in danger of disappearing into the ether and there was talk of Cowdenbeath becoming Rangers lite when Donald Findlay took over.