My DNA is only 18% English; I'm more Scandinavian than anything else, and more Celt than English...plus I have more than a dash (12%) of Eastern European
I'd never boo anyone's national anthem I don't think, but at the same time I'd never sing ours, because the wording is all about a supreme being (who I don't believe in) looking after our head of state (who I think should be replaced). May be a radical idea but I'd prefer a national anthem that was about the nation and just a little bit anthemic.
It does annoy me though that England use the British dirge when competing independently, while the other home countries use far more inspiring national songs, and we get lumbered with that crap servile rubbish.