Unauthorised occupant (8)
I believe the answer is:
squatter
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">unauthorised occupant</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 squatter that I've seen before include "Comparatively dumpy person" , "Someone occupies land illegally" , "person in illegal occupation" , "Someone who settles on land without right or title" , "Illegal occupier of empty property" .)