Wager miserable rozzers are authoritarian (3,4,3,3)
I believe the answer is:
lay down the law
'are authoritarian' is the definition.
(people laying down the law are being authoritative)
'wager miserable rozzers' is the wordplay.
'wager' becomes 'lay' (I've seen this in other clues).
'miserable' becomes 'down'.
'rozzers' becomes 'the law' (both can informally mean the police).
'lay'+'down'+'thelaw'='LAY DOWN THE LAW'
(Other definitions for lay down the law that I've seen before include "Issue instructions dogmatically" , "Read the Riot Act" , "Pontificate" , "Speak dogmatically" , "Be dogmatic" .)