The Scots shed some light on that in the Declaration of Arbroath in 1320.
“...Most Holy Father and Lord, we know and from the chronicles and books of the ancients we find that among other famous nations our own, the Scots, has been graced with widespread renown. They journeyed from Greater Scythia by way of the Tyrrhenian Sea and the Pillars of Hercules, and dwelt for a long course of time in Spain among the most savage tribes, but nowhere could they be subdued by any race, however barbarous. Thence they came, twelve hundred years after the people of Israel crossed the Red Sea, to their home in the west where they still live today. The Britons they first drove out, the Picts they utterly destroyed, and, even though very often assailed by the Norwegians, the Danes and the English, they took possession of that home with many victories and untold efforts; and, as the historians of old time bear witness, they have held it free of all bondage ever since.”
“...as long as but a hundred of us remain alive, never will we on any conditions be brought under English rule. It is in truth not for glory, nor riches, nor honours that we are fighting, but for freedom — for that alone, which no honest man gives up but with life itself.”
That fits with one of the theories I’ve read that the Celts that settled Ireland and Scotland came from Northern Spain approx 600 B.C.
Scholars called them “Celtiberians”.
CC
Phoenicians.