Police station is turned over (5)
I believe the answer is:
stasi
'police' is the definition.
(I have seen 'secret police' mean 'stasi' so perhaps 'police' could also mean 'stasi')
'station is turned over' is the wordplay.
'station' becomes 'sta' (I have seen 'Short station' mean 'sta' so perhaps 'station' could also mean 'sta').
'turned over' says the letters should be written backwards.
'is' backwards is 'si'.
'sta'+'si'='STASI'
(Other definitions for stasi that I've seen before include "Force that spied" , "old secret service" , "Secret police of the former German Democratic Republic" , "Former security force" , "East German Secret Police" .)