Blasted policeman stops old press chief (8)
I believe the answer is:
exploded
'blasted' is the definition.
(a blast is an explosion)
'policeman stops old press chief' is the wordplay.
'policeman' becomes 'plod' (UK informal term for a police officer).
'stops' is an insertion indicator.
'old' becomes 'ex' (prefix meaning former or onetime).
'press chief' becomes 'ed' (editor).
'ex'+'ed'='exed'
'plod' placed into 'exed' is 'EXPLODED'.
(Other definitions for exploded that I've seen before include "Burst violently" , "Blown up - no longer valid" , "Blew up" .)