Instant transfer back (6)
I believe the answer is:
second
I believe this clue is a triple definition!
'instant' is the first definition.
(I know that instant can be written as second)
'transfer' is the second definition.
(I've seen this before)
'back' is the third definition.
(both can mean to support an idea or proposal)
(Other definitions for second that I've seen before include "bit" , "Extra" , "honours degree" , "A duellist's or boxer's assistant" , "Support - a little time" .)