I don't think there's any comparison between the Nationalism of the Scots and Welsh and those who proclaim themselves to be English nationalists. I was born in England but consider myself to be British, I don't feel the need to assert my "Englishness" because basically I live in the most influential part of the United Kingdom. IMO flag waving English Nationalists are basically racist people trying to legitimise their racism. I'm always slightly amused by people talking about "English culture" again to legitimise their racism, google "English culture" the AI result is hilarious and certainly doesn't describe me or anyone I know!
Britain has been a diverse, multicultural country for a very long time, immigrants have enriched us, often initially doing the jobs that no one else wanted to do. They have been entrepreneurial, hard working and have encouraged their children to use education to improve their status in society. It's no accident that so many immigrant families have children who are doctors, lawyers, accountants and members of other prestigious professions. Yet, some in our population will seize upon the actions of a single person or a group of people, who behave very badly committing crimes that by anyone's standard are appalling, as being representative of a whole population of people with a particular ethnicity, when it is clearly, completely ridiculous. Bad people exist in every ethnic group including white people who have been born here.
So if you want to wave your St George's flag, by all means do but be aware that many people will see it for what it has become ie a declaration of xenophobia and racism not an attempt to reclaim it as a symbol of national pride.