Under no circumstances! (3,2,4,4)
I believe the answer is:
not on your life
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">under no circumstances</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for not on your life that I've seen before include "Like someone else's autobiography" , "No way!" , "There's no chance" , "On no account whatsoever" , "Emphatically, no!" .)