Note in constituency old rector and politician (7)
I believe the answer is:
senator
'politician' is the definition.
(I've seen this before)
'note in constituency old rector' is the wordplay.
'note' becomes 'n' (abbreviation**).
'in' means one lot of letters goes inside another.
'constituency' becomes 'seat' (I've seen this before).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'rector' becomes 'r'.
'n' put within 'seat' is 'senat'.
'senat'+'o'+'r'='SENATOR'
'and' acts as a link.
(Other definitions for senator that I've seen before include "US/Roman politician" , "US legislator" , "Member of upper house of legislature" , "Member of upper house commits treason?" , "One from uni's governing body" .)