It may be therefore that any imagined ethnic differences between different communities in the British Isles are just that - imagined.
No. Ethnic differences are more cultural than genetic.
EDITED FOR CLARITY
Ethnic differences more cultural than genetic? I suppose it depends on what you mean by "ethnic". If you are talking about "German" ethnicity and "Danish" ethnicity then I would agree. But what about "Northern European" and "Mediterranean" ethnicities. There are typically physical differences which are transmitted through inheritance rather than culture. I admit that these differences may be slight - a tendancy to a particular natural skin colour, a tendancy to a particular hair colour etc.
Lhuyd's argument (and this, of course, was pre-Mendel) was that the Atlantic coast celts came from a
different genetic heritage than the rest of the British Isles population, they were a different people from a different place. And that they were
physically different with a tendency towards red hair, stocky build, knobbly knees ...... God knows what.
And there are still people around believing this guff .....
My statement was a conclusion based on findings from the examination of DNA samples: no evidence of an invasion of central Europeans, of a different people, and a high level of genetic homogeneity amongst people from all parts of the British Isles - so no seperate "Celtic" genotype.
Of course "ethnic" differences in these circumstances are going to be cultural.