Head of government (5,8)
I believe the answer is:
prime minister
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">head of government</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 prime minister that I've seen before include "PM" , "Premier to brief clergyman" , "Senior political post" , "Law once in UK" , "May" .)