Unease of party politician with nothing certain (12)
I believe the answer is:
discomposure
'unease' is the definition.
(thesaurus)
'party politician with nothing certain' is the wordplay.
'party' becomes 'disco' (I've seen this before**).
'politician' becomes 'mp'.
'with nothing' becomes 'o' (I've seen this in other clues).
'certain' becomes 'sure' ('sure' can be a synonym of 'certain').
'disco'+'mp'+'o'+'sure'='DISCOMPOSURE'
'of' acts as a link.
(Other definitions for discomposure that I've seen before include "unease" , "Upset" .)