You’ll withhold consent? Rubbish! (6)
I believe the answer is:
refuse
'rubbish' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for refuse that I've seen before include "Turn down, reject" , "Pass up" , "Decline to accept - waste" , "Decline waste material" , "Waste, garbage" .)