Rule Conservative ignored before long (4)
I believe the answer is:
anon
'before long' is the definition.
(anon can mean soon)
'rule conservative ignored' is the wordplay.
'rule' becomes 'canon' (canon can mean a law).
'conservative' becomes 'C' (UK political abbreviation).
'ignored' indicates named letters should be taken away.
'canon' with 'c' taken out is 'ANON'.
(Other definitions for anon that I've seen before include "Immediately" , "Soon - unknown author (abbr)" , "devoid of credit" , "In the near future" , "Well-published writer" .)