The Arthurian tradition is Celtic, but Tolkien was a Saxon. The UK is made up of several difference countries - Wales, Scotland, North Ireland - these countries are Celtic, but England is Saxon. Saxon mythology is very similar to the norse tradition because they both stem from the larger Proto-Germanic ethnolinguistic culture and Old English poems like Beowulf and Deor make explicit reference to many of the gods, important individuals, cultural traditions, and events in the norse tradition. So while the Welsh had a culture hero in Arthur, the Saxon equivalents - Hengest and Horsa - barely anything is known about them in comparison. The poems they starred in were almost all destroyed and they're mostly known from historical records like the Anglo-Saxon Chronicle and a number of Roman sources which mention how they came to conquer the land which would later become England.
