Found up in Ullapool is a bitter herb (5)
I believe the answer is:
basil
'herb' is the definition.
(basil is a herb)
'found up in ullapool is a bitter' is the wordplay.
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'found' indicates a hidden word.
'lisab' is hidden within 'in ullapool is a bitter'.
'lisab' reversed gives 'BASIL'.
(Other definitions for basil that I've seen before include "Doctor of the fourth century" , "Name of male" , "Aromatic leaves, used fresh or dried" , "Pesto ingredient" , "Aromatic herb with purplish-green leaves" .)