The full size promotional photo available at Merlin's Keep: www.farfarawaysite.com/merlin
photo
merlin
This Merlin sur la BBC photo contains
manteau, capote, manteau à capuchon, opéra manteau, opéra hotte, manteau d'opéra, opéra, manteau d’opéra, and hotte opéra.
There might also be
surcoat and surcot.