There were indigenous people in the British Isles before the Celts arrived, from Spain I believe it was. There was inbreeding among the Picts and others after they arrived so the group was a bit different by the time the Romans showed up.
There are cairns and obelisks in Ireland and Scotland that are older than the pyramids of Egypt, to me that's way more interesting than another group of immigrants showing up centuries later, but it's all fun research really.
As far as the "hating Hebrews" thing, sounds more like the effects of a more contemporary issue, that being the catholic church's official position towards Jews up until 1964. I haven't come across too much "ancient" antisemitism, but then my library is focused in other directions.