I always think people feel you have to be born in England specifically to be 'English' (not British) and then even English people might not consider many people English even if they were (for example, most EM people - see what happened when a trio of Black English lads messed up a bit in an England football tournament).
I was born in England but have never called myself English : I don't consider myself remotely English. No one English has ever called me English either except to wind me up. DH was born in England, too, but spent his whole childhood in South Wales. Never considered himself Welsh. I guess football teams made a big difference to him.
I am sure, however, that this entitles me according to Derxa Law to Have An Opinion. The flags were put up because of Little Englander anti immigration rhetoric. In Scotland, the wave of lamppost flags was copying the English movement. Normal non lamppost flag flying there (and maybe also in England although I am less convinced) is national pride. See also: Wales.