Effect of one parliamentary bill introduced by member (6)
I believe the answer is:
Here is my best explanation:
'effect' is the definition.
(impact is a kind of effect)
'one parliamentary bill introduced by member' is the subsidiary indication.
'one' becomes 'i' (roman numeral).
'parliamentary bill' becomes 'act'.
'introduced by' is a charade indicator (letters next to each other).
'member' becomes 'mp'.
'act' put after 'mp' is 'mpact'.
'of' is the link.
(Other definitions for impact that I've seen before include "Effect - collision", "Collision - effect", "Force of blow or collision", "Forceful contact between two objects", "The striking of one thing against another", "Repercussion", "Forcible contact; marked influence", "Force of colllision or blow", "Force exerted by collision" and "Crash".)