It was the Dumnonii who inhabited what is now Cornwall and Devon - and sections of Somerset and Dorset.
...
These various folk, and other Celtic tribes, shared a common language, and all, of course, came from mainland Europe.
The Celts weren't the first people on the Island, they were the first invaders thereof. ... Chronology is everything, when it comes to history.
The Long-Before-Celtic Tribes of Britain
"Strabo reports of Posidonius ... 'The Cassiterides are ten in number, and lie near each other in the ocean, towards the north from the haven of the Artabri: one of them is desert, but the others are inhabited by men in black cloaks, clad in tunics reaching to the feet, and girt about the breast; walking with staves, and bearded like goats. They subsist by their cattle, leading for the most part a wandering life. And having metals of tin and lead, these and skins they barter with the merchants for earthenware and salt, and brazen vessels.' ...
Solinus ... states that 'a stormy channel separates the coast which the Damnonii occupy from the island Silura, whose inhabitants preserve the ancient manners, reject money, barter merchandise, value what they require by exchange rather than by price, worship the gods, and both men and women profess a knowledge of the future.'...
Firbolg and Firdomnan harmonises very singularly with the legendary accounts of the tin workers of Cornwall and the tin islands. It is not difficult to recognise in the tradition that the Firbolg derived their name from the leathern sacks which they filled with soil, and with which they covered their boats, and the Firdomnan from the pits they dug, the people who worked the tin by digging in the soil and transporting it in bags to their hide-covered boats."
--Skene, Celtic Scotland,v1
"The extension of this non-Aryan race through France, Spain, and Britain, in ancient times, based solely on the evidence of the human remains, is confirmed by an appeal to the ethnology of Europe within the historic period. In the Iberian peninsula the Basque populations of the west are defined from the Celtic of the east by the Celtiberi inhabiting the modern Castille (see Map, Fig. 68). In Gaul the province of Aquitania extended as far north, in Caesar's time, as the river Garonne, constituting the modern Gascony, to which was added, in the days of Augustus, the district between that river and the Loire; a change of frontier that was probably due to the predominance of Basque blood in a mixed race in that area similar to the Celtiberi of Castille. The Aquitani were surrounded on every side, except the south, by the Celtae, extending as far north as the Seine, as far to the east as Switzerland and the plains of Lombardy, and southwards, through the valley of the Rhone and the region of the Volcae, over the Eastern Pyrenees into Spain. The district round the Phocaean colony of Marseilles was inhabited by Ligurian tribes, who held the region between the river Po and the Gulf of Genoa, as far as the western boundary of Etruria, and who probably extended to the west along the coast of Southern Gaul as far as the Pyrenees. They were distinguished from the Celtae, not merely by their manners and customs, but by their small stature and dark hair and eyes, and are stated by Pliny and Strabo to have inhabited Spain. They have also left marks of their presence in Central Gaul in the name of the Loire (Ligur), and possibly in Britain in the obscure name of the Lloegrians. They invaded Sicily as the Sikelians, and if the latter be identified with the Sikanians considered by Thucydides and other writers to be of Iberian stock, it will follow that they are a cognate race. Their stature and swarthy complexion, as well as the ancient geographical position conterminous with the Iberic population of Gaul and Spain, confirm this conclusion. The non-Aryan and probably Basque population of Gaul was therefore cut into two portions by a broad band of Celts, which crosses the Eastern Pyrenees, and marks the route by which the Iberian peninsula was invaded."
--Dawkins, Cave Hunting
VII. The three Social Tribes of the Isle of Britain. The first was the nation of the Cymry, that came with Hu the Mighty into the isle of Britain, because he would not possess lands and dominion by fighting and pursuit, but through justice and in peace. The second was the tribe of the Lloegrwys, that came from the land of Gwasgwyn, being descended from the primitive nation of the Cymry. The third were the Brython, who came from the land of Armorica, having their descent from the same stock with the Cymry. These were called the three Tribes of Peace, on account of their coming, with mutual consent, in peace and tranquillity: and these three tribes were descended from the original nation of the Cymry, and were of the same language and speech.--Cambro-Briton, v1
