Break off from detective’s son permanently (8)
I believe the answer is:
dissever
'break off' is the definition.
'detective's son permanently' is the wordplay.
'detective's' becomes 'dis' (Detective Inspector).
'son' becomes 's'.
'permanently' becomes 'ever'.
'dis'+'s'+'ever'='DISSEVER'
'from' acts as a link.
(Other definitions for dissever that I've seen before include "split apart" , "divide into parts" , "Cut apart" .)