Announce PM's retired in utter shambles (7)
I believe the answer is:
trumpet
'announce' is the definition.
(both can mean to proclaim)
'pm's retired in utter shambles' is the wordplay.
'retired' is a reversal indicator.
'in' is an insertion indicator.
'shambles' is an anagram indicator.
'pm' written backwards gives 'mp'.
'utter' with letters rearranged gives 'truet'.
'mp' placed within 'truet' is 'TRUMPET'.
(Other definitions for trumpet that I've seen before include "Shout!" , "Centre of daffodil flower" , "Metal wind instrument" , "Loud cry" , "Brass musical instrument" .)