Effect of legislation introduced by one politician (6)
I believe the answer is:
impact
'effect' is the definition.
(I know that impact is a type of effect)
'legislation introduced by one politician' is the wordplay.
'legislation' becomes 'act' (I've seen this in another clue).
'introduced by' means one lot of letters go next to another.
'one' becomes 'i' (Roman numeral).
'politician' becomes 'mp' (Member of Parliament).
'i'+'mp'='imp'
'act' put after 'imp' is 'IMPACT'.
'of' acts as a link.
(Other definitions for impact that I've seen before include "Marked effect or influence" , "Impression" , "The force of one body against another" , "Forceful contact between two objects" , "Forcible contact; marked influence" .)