@Pollyputhekettleon I'm not a rugby person either, but you bringing up a specific tournament doesn't add to your argument.
Lists of countries officially worldwide ISN'T based on sports tournaments. By the way, the term "nation" DOES mean country.
I repeat, England, Scotland, Wales and Northern Ireland are non-sovereign countries. Therefore, English, Scottish, Welsh and Northern Irish are all REGIONAL identities.
Why are they regional identities and NOT nationalities?
Because they are actually regions of a SINGLE unitary sovereign state known as the United Kingdom of Great Britain and Northern Ireland.
Countries were formed via war between their constituent parts. For example, Satsuma prefecture in Japan was its own independent country for centuries before Japan was unified into one country by force. France is another good example of this nation building too - French wasn't originally the language spoken widely across France as we know it today. It was a minority language, but became the dominant, unifying language for all France following unification via force. English language follows the same pattern found right across European nation building.
The nationality of all persons born or to parents who are citizens of the United Kingdom IS actually British.
Unlike other countries such as France, the UK retained its constituent parts as HISTORIC non-sovereign countries with English, Scottish, Welsh and Northern Irish being regional identities.
The case of Emma DeSouza in Northern Ireland demonstrates what I said. She lost her case and British Nationality Act 1981 is still in force. So, in Northern Ireland the Irish identity is also a regional identity - being able to hold an Irish passport doesn't change that.