Church supporting transgression until now (5)
I believe the answer is:
since
'until now' is the definition.
(thesaurus)
'church supporting transgression' is the wordplay.
'church' becomes 'ce' (abbreviation for Church of England).
'supporting' says to put letters next to each other (in a down clue, some letters go below others).
'transgression' becomes 'sin' (sin is a kind of transgression).
'ce' after 'sin' is 'SINCE'.
(Other definitions for since that I've seen before include "Because; ago" , "Seeing that" , "in the past" , "From that time one" .)