Saint George was Syrian
One of the useful things history does is laugh at people who stake a claim. Any restraints on free movement of people, goods, capital, and ideas is temporary. We know we are very different to our parents and siblings, so the idea that there is any separate group identity that is not just a flimsy story is bizarre. I have spent the morning in the British Museum with some friends who live in Seoul, South Korea, and teach English. One is South African, and one is American. Both have red hair. There was a map in one section on the history of the UK which made me chuckle. More a gutted chuckle than a haha chuckle. The people who have 'the biggest claim' to the UK are the Celts of Wales, Ireland and Scotland. The Anglo-Saxons were very European immigrants. Saint George was Syrian. But if Celts stake a claim, history will also laugh. The Celts themselves came from Europe way before that. Most of them get that.
If you lay claim to culture, history will laugh. How we learnt to hunt, speak, farm, write, travel, build, love, fight, eat and drink has always been a communal effort of Global Citizens.
The Celts spread from the Yellow bit
The Dark Green is where Celtic languages remain widely spoken