Got rid of a sitting member, a horror of mine (8)
I believe the answer is:
firedamp
'a horror of mine' is the definition.
(mining hazard)
'got rid of a sitting member' is the wordplay.
'got rid of' becomes 'fired' (I've seen this before).
'sitting member' becomes 'mp' (Member of Parliament).
'fired'+'a'+'mp'='FIREDAMP'
(Other definitions for firedamp that I've seen before include "Combustible mixture" , "Explosive gas in mines" , "Methane found in coal mines" , "Coal mine peril" , "a particular horror of mine" .)