Free rein (5,7)
I believe the answer is:
carte blanche
'free rein' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for carte blanche that I've seen before include "Free hand" , "Complete discretion" , "Complete freedom to act as one wishes" , "Unrestricted authority" , "Complete freedom of action" .)