Nick is working under electoral system (6)
I believe the answer is:
prison
'nick' is the definition.
(British slang)
'is working under electoral system' is the wordplay.
'working' becomes 'on' (on can mean working or activated).
'under' is a charade indicator (letters next to each other).
'electoral system' becomes 'pr' (I've seen this in other clues).
'is'+'on'='ison'
'ison' put after 'pr' is 'PRISON'.
(Other definitions for prison that I've seen before include "Nick" , "Penitentiary" , "Wormwood Scrubs, for example" , "Correctional institution" , "cage" .)