Pilgrim. As the prologue states :
Off all the tales told of these isles few are as strange as that of William Palmer. Cursed, apparently, on the road to Canterbury in the spring of 1185 for denying the presence of the other world by the king of the Grey Folk - or Faerie - himself, and compelled to walk from that day to this between the worlds of magic and men, and subsequently known in all the strange and wonderful lore attributed to the mysterious William Palmer, as Pilgrim.
A man cursed with immortality who, now in a modern setting , battles with incursions into this world from creatures from without, whilst seeking an end to his existence of 900 years.
If you have an interest in British mythology, customs and folklore this is highly recommended ; quite dark and matter of fact in its telling.
All of the series (5) are currently available for a few weeks on the IPlayer.