Am I the only one that read the OP’s intent as “everyone who is ethnically British or Irish”, that is to say, “Does everyone who is ethnically English/Welsh/Cornish/Scottish/Irish inherently have Scandinavian genes as well”, rather than the absurd question everyone else is assuming, “Does everyone who resides within the United Kingdom or the Republic of Ireland have Scandinavian ancestry”?
Ethnicity is culture, not genetics or race. There are ethnically British and Irish people who are not at all white. That’s what people are objecting to: that somehow the people with deep genetic roots on the island are more British than the people who don’t have deep genetic roots on the island.
Americans in particular use “ethnically” as a way to avoid the term “racially,” and tend to speak as if ethnicity were heritable. It can be passed down from parent to child, but it’s not heritable.
Okay, fine, so replace “ethnically” in my post with “racially” or “genetically” or “cladistically” or whatever word you need to interpret the question as “Did Scandinavian genes mix so thoroughly into the population of the British Isles that all descendants of the population of those isles at the time are of partial Scandinavian ancestry?”. Whatever word you prefer, I have my doubts that the OP literally meant to ask the question everyone is answering, which is whether people who moved to the United Kingdom from Sri Lanka or wherever and attained citizenship have Scandinavian ancestry just because they’re now British. That question is obvious nonsense, though if that is indeed what the OP meant, they are invited to tell me I’ve misinterpreted the question.
I’m sure that is what the OP intended, but since immigration to the UK has been more or less continual throughout history, there is nowhere to draw the bright line of distinction between people ‘from’ here and ‘not from’ here.
I mean, that’s how we got the Scandinavian genes.
That’s fine, but it’s a different question. One of the ways of combatting racism is to call people on their well-meaning but incorrect assumptions. Excluding the statistical minority in an offhand, casual way reinforces the idea that they are somehow less authentic. When you picture a generic American, chances are decent that it’s a white male: why not a black woman? Would she be any less American? Of course not.
No single example of this matters, but the pattern matters a lot. It’s impossible to change the pattern without challenging the instances one at a time. So: yes, I know what the OP meant. No, I don’t think the OP meant anything wrong. Yes, I think there’s value in getting him / her to reformulate the question to reflect what they’re actually asking.
OK, sorry, just re-read post#23 and yes, that’s a question that could have a firm answer (are there any British descendants of the people who were around at the time of the Vikings, who are as yet unmixed with people of Viking descent), but I am not sure the OP was asking that.