Spot politician going into mansion (6)
I believe the answer is:
pimple
'spot' is the definition.
(I've seen this before)
'politician going into mansion' is the wordplay.
'politician' becomes 'mp'.
'going into' means one lot of letters goes inside another.
'mansion' becomes 'pile' (I've seen this in other clues).
'mp' going into 'pile' is 'PIMPLE'.
(Other definitions for pimple that I've seen before include "Small pustule" , "Inflamed skin spot" .)