Xin, My origins are British for as far back as I can go, nearly all from London and Home Counties, with one exception, my 4G grandfather born in Ireland. If you think about it, this accounts for 1/64 of my tree, 4/128 (1/32) if his parents and grandparents etc were all from Ireland. So, about 3% of my ancestry.
My ethnicity at Ancestry shows 48% Western European, 33% Great Britain, 12% Ireland/Scotland/Wales, 3% Iberian Peninsula, 1% Scandinavian, plus a few minorities.
This may reflect ancestry from the way distant past, as GB was colonised by many different countries, but does not reflect my ethnicity for the past 200 - 300 years.
At other sites my ethnicity shows differently, but I am only vaguely interested in my roots from thousands or even millions of years ago.
As has been said on this thread and others, the ethnicity reports are next to useless, but it it is considered one of the main selling points. My next door neighbour has had it done for this reason alone, not interested in family history at all. She is in for a big disappointment, I think.
Regards Margaret