Every parish church in England (more or less) has flown the St. George's cross traditionally for as long as I can remember. There is nothing wrong with that. Conversely, Union Jacks are a major symbol of Loyalism and Orangeism in Ireland, and parts of Scotland, which is an extremely aggressive and "hands on" movement. Union Jacks can be seen in pictures of every far right movement going back a century or more.

The Union Jack is a symbol of empire and colonialism which the St. George's Cross isn't.

However, the football thing is more recent. If you watch "the Italian Job" from the 1960s, the England fans wave around Union Jacks instead of their own specific flag (as Scotland and Wales fans would). Clearly in the intervening years, England fans have discovered the England flag.

Scottish and Welsh people seem to be a lot more comfortable with their identity than English do. And that includes their flags. I have seen countless bits of research which suggest that ethnic minorities happily identify as Scottish and Welsh in Scotland and Wales, but in England, they identify as British rather than English. I suggest you read Billy Bragg's "the Progressive Patriot". He is an English socialist who has tried to reclaim English identity from the far right, which he is entitled to.

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".