Slight consequence of Chamberlain's ultimatum being largely ignored (6)
I believe the answer is:
insult
'slight' is the definition.
(I've seen this before)
'chamberlain's ultimatum being largely ignored' is the wordplay.
'being largely ignored' indicates a hidden word (most of the letters must be ignored).
'INSULT' is hidden within 'chamberlains ultimatum'.
'consequence of' is the link.
(Other definitions for insult that I've seen before include "Remark intended to hurt or humiliate" , "Demeaning remark" , "A deliberately offensive remark" , "An addition to injury?" , "Hurtful and offensive remark" .)