Legislator blocking current law's effect (6)
I believe the answer is:
impact
'effect' is the definition.
(impact is a kind of effect)
'legislator blocking current law's' is the wordplay.
'legislator' becomes 'mp' (I've seen this in other clues).
'blocking' means one lot of letters goes inside another.
'current' becomes 'i' (symbol for electric current).
'law' becomes 'act' (I've seen this before).
'i'+'act'='iact'
'mp' put into 'iact' is 'IMPACT'.
(Other definitions for impact that I've seen before include "The striking of one thing against another" , "Force or shock of a collision" , "Bear upon" , "Forceful striking" , "The force of one body against another" .)