If head chorister is in possession of the neckwear, they say they might reprimand him (8)
I believe the answer is:
chastise
'reprimand him' is the definition.
'chastise' can be an answer for 'reprimand' (chastising is a kind of reprimanding). I am not sure about the 'him' bit.
'if head chorister is in possession of the neckwear they say they might' is the wordplay.
I cannot really understand how this works, but
'is' is within the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found in the answer.
'say' could be 'as' (I've seen this in other clues) and 'as' is found in the answer.
The remaining letters 'che' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for chastise that I've seen before include "Whip perhaps" , "Teach Sis to scold" , "discipline" , "lecture" , "Scold severely" .)