I don't think anyone is claiming that Rishi Sunak isn't a UK citizen, but he certainly isn't a member of the English ethnic group, or any of the Celtic ethnic groups that also make up the UK's native population.
[0] https://en.wikipedia.org/wiki/English_people
[1] https://en.wikipedia.org/wiki/History_of_the_monarchy_of_the...
England hasn't had an English king since 1066, that's not controversial, and even then the inbreeding between the European royal houses was creating a pan-european elite that made world world 1 more of a really bad family argument than anything else.
What's really odd is that Rishi Sunak is extremely proud of his ethnicity and heritage, it's unfortunate that we've made it almost impossible for other people's to have that same pride.
No-one questions the Englishness of white men born in England to two non-English parents. People raising the absurd non-issue of Rishi Sunak’s Englishness are just concealing their rather obvious prejudices with a lot of bafflegab about ‘English ethnicity’ (a concept which not even they can really take at all seriously, if they at least have some acquaintance with English history).
Rushi Sunak ancestry is obviously Indian. I don't really care about his ethnicity (he another politician in a suit to me), but I can understand what people mean when they say he isn't English without automatically assuming they are Racist.
Denying the existence of an ethic group is extremely racist, and is often considered a precursor to other much more serious issues.
If you have any acquaintance with English history you would be well aware that there are native ethnic groups that have been in the UK since approximately the end of the younger dryas around 11,000 years ago.
The last major migration was the anglo-saxons around 1500 years ago.
These groups still exist and the majority of the UK population can still trace their origin back to one of these groups.
And you'd be aware that nothing even vaguely corresponding to 'England' existed 11,000 years ago. If you are willing to lump the descendants of Romans, Normans, Jutes, Durotriges, Iceni, Vikings, etc. together into one group and call them all 'English' just because they happened to live in the territory of what is now England, then you've already conceded the point that the identity is national, not ethnic.
But hey, over in the other thread you are denying that Boris Johnson is English, so it's clear that you have a rather eccentric concept of the category.
The English ethnic group is defined by a shared genetics and culture, the English enthic group isn't just political it is biological and can be identified via DNA.
I wouldn't consider my definition eccentric, it's based on the UN defintion: Ethnic group or ethnicity refers to a group of people whose members claim a common heritage or common ancestry and usually speak a common language and may have some common cultural practices.
The other thread argued that Boris Johnson is ethnically Turkic (I have no idea if that is true) on the assumption it is true, Boris Johnson may meet the requirement of a common language, but does not meet the requirement of a shared ancestry to be ethnically English.
Many of the groups that you mentioned existed in the UK over 1000 years ago, and shared in the same invasions, same issues, and developed a shared culture due to that shared history and closeness of relations, and of course as evidenced by DNA analysis interbreeding.
So yeah I would say that in the space of a millennium multiple groups can become one group.
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