Knock-on consequences (6,6)
I believe the answer is:
domino effect
'knock-on consequences' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for domino effect that I've seen before include "Consequence of one event setting off a chain of similar ones" , "One falls, all fall" , "series of knock-ons" , "Each event being a consequence of the previous one" , "Knock-on consequences" .)