Withdraw officially (6)
I believe the answer is:
secede
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">withdraw officially</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for secede that I've seen before include "Formally achieve independence" , "Disaffiliate" , "'Withdraw, break away (6)'" , "Formally withdraw (from federal union)" , "Withdraw (from a federal union or organisation)" .)