Denounce former partner, City judge (8)
I believe the answer is:
execrate
'denounce' is the definition.
(I've seen this before)
'former partner city judge' is the wordplay.
'former partner' becomes 'ex' (an ex-partner).
'city' becomes 'EC' (the City of London postcode).
'judge' becomes 'rate' (rating is a kind of judging).
'ex'+'ec'+'rate'='EXECRATE'
(Other definitions for execrate that I've seen before include "Deplore and detest" , "Denounce or detract" , "Express great loathing for" , "Curse" , "Express hatred for" .)