Went in pursuit of 400, accepting Ashes nearly lost (6)
I believe the answer is:
'went in pursuit of' is the definition.
(I've seen this in another clue)
'400 accepting ashes nearly lost' is the wordplay.
'400' becomes 'cd' (I can't justify this - if you can you should believe this answer much more).
'accepting' means one lot of letters goes inside another (inserted letters are accepted).
'nearly' means to remove the last letter.
'lost' indicates an anagram.
'ashes' with its final letter taken away is 'ashe'.
'ashe' anagrammed gives 'hase'.
'cd' placed around 'hase' is 'CHASED'.
Can you help me to learn more?
(Other definitions for chased that I've seen before include "Pursued at speed" , "Hunted" , "Decorated metal with engraved or embossed work" , "Wooed" , "Pursued or engraved" .)