Go before City editor blocks advance payment (8)
I believe the answer is:
antecede
'go before' is the definition.
(thesaurus)
'city editor blocks advance payment' is the wordplay.
'city' becomes 'ec' (the City of London postcode).
'editor' becomes 'ed'.
'blocks' indicates putting letters inside (the inside letters form a 'blockage').
'advance payment' becomes 'ante' (I've seen this before).
'ec'+'ed'='eced'
'eced' put into 'ante' is 'ANTECEDE'.
(Other definitions for antecede that I've seen before include "go before, in rank" , "Lead" .)