The Cwn Annwn
The Cwn Annwn, which means hounds of the otherworld (underworld), are Welsh phantom dogs seen as a death portent. Their growling is louder when they are at a distance, and as they draw near the growling grows softer and softer.
Annwn is the Welsh underworld, a place ruled by Gwyn ap Nudd or by Arawn, who is one in the same character. In Welsh stories this land is the ever-living, and is full of magical beasts and treasures.
Almost every area in Britain has its version of phantom or fairy dogs.