Be the Chancellor: mostly disagreeable (8)
I believe the answer is:
liverish
'disagreeable' is the definition.
(I've seen this in another clue)
'be the chancellor mostly' is the wordplay.
I cannot really see how this works, but
'be' could be 'live' (to be is to live or exist) and 'live' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for liverish that I've seen before include "slightly ill" , "Like foie gras" , "Dyspeptic" , "Irritable as from bodily disorder" , "a bit off?" .)