Command police department returning to gallery (7)
I believe the answer is:
dictate
'command' is the definition.
(thesaurus)
'police department returning to gallery' is the wordplay.
'police department' becomes 'cid' (I've seen this in other clues).
'returning' says the letters should be written backwards.
'to gallery' becomes 'tate' (I've seen this before).
'cid' back-to-front is 'dic'.
'dic'+'tate'='DICTATE'
(Other definitions for dictate that I've seen before include "Command" , "Order; determine" , "Determine; read out to be taken down" , "say" , "Issue commands" .)