The Germanic Tribes
Celtic influence and language eventually died out under Roman and later Germanic influence. Most of the Celtic speakers were pushed west and north by the invaders - mainly into what is now Wales, Scotland and Ireland, which is where the last remaining Celtic languages, - Welsh, Scots Gailic and Irish Gailic, have survived in coutryside areas and are still taught in local schools.
The Irish Sea in fact effectively isolated Ireland from the continent and from Roman conquest. Here, shielded and removed, Ireland developed in isolation. Today the original British Celtic heritage can be seen in the ruins of Celtic