Government policy co-ordinator that's arguably not all there (4)
I believe the answer is:
tsar
'government policy co-ordinator' is the definition.
(in posts like drugs tsar, equality tsar, etc)
'that's arguably not all there' is the wordplay.
'not all there' says the answer is hidden in the clue (only some of the letters are to be retained).
'TSAR' is hidden in the letters of 'thats arguably'.
(Other definitions for tsar that I've seen before include "Tyrant" , "Title given to the kings of Bulgaria" , "Supreme authority" , "Peter the Great, for example" , "Rats to the Russian emperor" .)