Register as a member (5)
I believe the answer is:
enrol
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">register as a member</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for enrol that I've seen before include "Join up, sign on" , "Enlist" , "Loner inclined to join in" , "Record" , "Join as member" .)