British writer commented endlessly about King (4)
I believe the answer is:
saki
'british writer' is the definition.
'saki' can be an answer for 'writer' (I've seen this before). I am unsure of the 'british' bit.
'commented endlessly about king' is the wordplay.
'commented endlessly' becomes 'sai' (I can't justify this - if you can you should give a lot more credence to this answer).
'about' is an insertion indicator.
'king' becomes 'k' (abbreviation for king in chess).
'sai' enclosing 'k' is 'SAKI'.
Can you help me to learn more?
(Other definitions for saki that I've seen before include "Author H. H. Munro's pseudonym" , "drink in Tokyo" , "Monkey; author" , "Rice < monkey" , "refreshment for Orientals" .)