Tory going down as offensively patronising (13)
I believe the answer is:
condescending
'offensively patronising' is the definition.
(I've seen this before)
'tory going down' is the wordplay.
'tory' becomes 'con' (abbreviation for conservative).
'going down' becomes 'descending' ('descend' can be a synonym of 'go down').
'con'+'descending'='CONDESCENDING'
'as' acts as a link.
(Other definitions for condescending that I've seen before include "Showing (to others) that one feels superior" , "Toffee-nosed" , "Snooty" , "Supercilious" , "Offensively patronising" .)