A politician receiving duke without preparation (2,3)
I believe the answer is:
ad lib
'without preparation' is the definition.
(I've seen this before)
'a politician receiving duke' is the wordplay.
'politician' becomes 'lib'.
'receiving' is an insertion indicator.
'duke' becomes 'd'.
'a'+'lib'='alib'
'alib' placed around 'd' is 'AD-LIB'.
(Other definitions for ad lib that I've seen before include "Off-the-cuff remark" , "As You Like It?" , "Perform without a script" , "Speak unprepared" , "with no forethought" .)