In his series, "Song of Ice and Fire", George R.R. Martin re-imagines a War of the Roses era-Britain where the British Isle is greatly enlarged and the continent compressed. He creates a history that mirrors the waves of historical migration ("First Men" for the Picts, and the "Andals" and the "Rhoynar" for the Angles and Saxons--Rhoyne is a combination of Rhine and Rhone.) He has a later invader, the Valyrians, take over rule of the island in similar fashion to the Normans under William the Conqueror. The island is divided by a massive wall in roughly the same place as the Antonine Wall. In terms of the supernatural, he creates the "Children of the Forest", who literally live under hills, as an analogue of the fairy folk. He also utilizes the undead as an adversary against mankind.
Is there any precedent for a mythology of the undead in the British Isles?
I know a little about Arawn and the Norse Draugr, but haven't yet found any specific stories.