A much smaller percentage of the men in the British Isles belong to the I haplogroup, which split from the J haplogroup (very common in the Near East) upwards of 30,000 years ago. The I haplogroup is found in the Balkans before the last glacial maximum. During the height of the Ice Age, only southern parts of Europe were inhabited such as the Balkans, Italy and the Iberian peninsula. After the Ice Age ended, men with the I-haplogroup moved north, some to Scandinavia, and their descendants may have carried the I-group to the British Isles (Hagar and his buddies). The I group remains very common today in the Balkans.
“…languages can be imposed by a small minority…”
Irish (i.e., Gaelic) does not have a simplified grammar such English or Spanish which is what we would expect for an imposed language. It’s a language that is learned at one’s mother’s knee.