Formal pronouncement by police, turning on corporation (6)
I believe the answer is:
dictum
'formal pronouncement' is the definition.
(I've seen this before)
'police turning on corporation' is the wordplay.
'police' becomes 'CID' (abbreviation for Criminal Investigation Department).
'turning' is a reversal indicator.
'on' says to put letters next to each other.
'corporation' becomes 'tum' ('corporation' can humorously mean belly fat).
'cid' back-to-front is 'dic'.
'dic'+'tum'='DICTUM'
'by' acts as a link.
(Other definitions for dictum that I've seen before include "A Latin saying or formal expression of opinion" , "Short statement of a general principle" , "firm statement" , "Popular maxim" , "Authoritative pronouncement" .)