MP and constituent (6)
I believe the answer is:
member
I believe this clue is a double definition.
'mp' is the first definition.
(Member of Parliament)
'constituent' is the second definition.
(I know that member is a type of constituent)
'and' acts as a link.
(Other definitions for member that I've seen before include "Limb, MP" , "Limb - affiliate" , "Limb - person belonging to a group" , "Limb; society joiner" , "Eg, leg, arm" .)