Advocate coppers should have jurisdiction (6)
I believe the answer is:
preach
'advocate' is the definition.
(I know that advocate can be written as preach)
'coppers should have jurisdiction' is the wordplay.
'coppers' becomes 'p'.
'should have' says to put letters next to each other.
'jurisdiction' becomes 'reach' (I've seen this in another clue).
'p'+'reach'='PREACH'
(Other definitions for preach that I've seen before include "Lecture" , "A perch (anag.)" , "Do as Amos Starkadder did" , "Moralise" , "Take the moral high ground" .)