Spot big house occupied by politician (6)
I believe the answer is:
pimple
'spot' is the definition.
(I've seen this before)
'big house occupied by politician' is the wordplay.
'big house' becomes 'pile' (term for a large or fancy house).
'occupied by' indicates putting letters inside (inserted letters occupy or enter the word).
'politician' becomes 'MP' (Member of Parliament).
'pile' enclosing 'mp' is 'PIMPLE'.
(Other definitions for pimple that I've seen before include "Small pustule" , "Inflamed skin spot" .)