Tetchy taxi driver collects Republican (6)
I believe the answer is:
crabby
'tetchy' is the definition.
'taxi driver collects republican' is the wordplay.
'taxi driver' becomes 'cabby' (I've seen this before).
'collects' is an insertion indicator.
'republican' becomes 'r' (abbreviation).
'cabby' enclosing 'r' is 'CRABBY'.
(Other definitions for crabby that I've seen before include "Bad-tempered, irritable" , "Temperamental" , "Irritable - like a crustacean?" , "Bad-tempered like common crustacean" , "Sour and cantankerous like common shellfish" .)