Diversity, My Ass!
(media.scored.co)
I would suspect that anyone from the British isles with black hair and brown eyes actually has Spanish/Berber admixture, like the so-called "black Irish". The reason they show up as "100% British" in DNA tests is that the results for those tests are based on how reference subjects self-identified. For example, if a "black Irish" person self-identified as pure Irish in the test's reference matrix, then any "black Irish" person who takes the test is going to get back a pure Irish result.