People mostly accepting National Insurance model (8)
I believe the answer is:
mannikin
'model' is the definition.
'people mostly accepting national insurance' is the wordplay.
I cannot quite understand how this works, but
'people' could be 'man' (I've seen this in other clues) and 'man' is located in the answer.
'national' could be 'n' (abbreviation listed in Chambers) and 'n' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for mannikin that I've seen before include "Anatomical model - dwarf - child" , "Little chap" , "minor fellow" , "Clothes dummy" .)