Whitehall monument (8)
I believe the answer is:
cenotaph
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">whitehall monument</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 cenotaph that I've seen before include "Tomb-like monument to people buried elsewhere" , "Empty tomb" , "Feature of Whitehall" , "construction in Whitehall" , "What divides Whitehall" .)