Effect of one parliamentary bill introduced by member (6)
I believe the answer is:
impact
'effect' is the definition.
(impact is a kind of effect)
'one parliamentary bill introduced by member' is the wordplay.
'one' becomes 'i' (Roman numeral).
'parliamentary bill' becomes 'act'.
'introduced by' is a charade indicator (letters next to each other).
'member' becomes 'mp'.
'act' after 'mp' is 'mpact'.
'i'+'mpact'='IMPACT'
'of' acts as a link.
(Other definitions for impact that I've seen before include "Collision - effect" , "hit, in a big way" , "Force of blow or collision" , "Forcible contact between two things" , "The striking of one body against another" .)