Spot man in house holding bomb? On the contrary (6)
I believe the answer is:
pimple
'spot' is the definition.
(I've seen this before)
'man in house holding bomb? on the contrary' is the wordplay.
'man in house' becomes 'MP' (Member of Parliament in the House of Commons).
'holding' is an insertion indicator.
'bomb? on the contrary' becomes 'pile' (I can't explain this - if you can you should give a lot more credence to this answer).
'mp' going inside 'pile' is 'PIMPLE'.
(Other definitions for pimple that I've seen before include "Small pustule" , "Inflamed skin spot" .)