Area police officer lacking flexibility (8)
I believe the answer is:
district
'area' is the definition.
(I've seen this before)
'police officer lacking flexibility' is the wordplay.
'police officer' becomes 'DI' (detective inspector).
'lacking flexibility' becomes 'strict' (I am not sure about this - if you are sure you should believe this answer much more).
'di'+'strict'='DISTRICT'
Can you help me to learn more?
(Other definitions for district that I've seen before include "London Underground line represented in green" , "Territorial division" , "'Area, territory (8)'" , "Area, region" , "Region marked off for administrative or other purposes" .)