Hint about Labour's leader produces shock (4)
I believe the answer is:
jolt
'shock' is the definition.
(thesaurus)
'hint about labour's leader' is the wordplay.
'hint' becomes 'jot' ('jot' can be a synonym of 'hint'**).
'about' is an insertion indicator.
'leader' suggests taking the first letters.
The first letter of 'labours' is 'l'.
'jot' going around 'l' is 'JOLT'.
'produces' acts as a link.
(Other definitions for jolt that I've seen before include "elbow" , "bump" , "Sudden shock" , "Sudden jerk" , "Sudden impact" .)