Permission to proceed with new journey, heading off (5,5)
I believe the answer is:
green light
'permission to proceed' is the definition.
(I've seen this before)
'with new journey heading off' is the wordplay.
'with' is a charade indicator (letters next to each other).
'new' becomes 'green' (I've seen this in another clue).
'journey' becomes 'flight' (flight is a kind of journey).
'heading off' means to remove the first letter.
'flight' with its initial letter removed is 'light'.
'green' next to 'light' is 'GREEN LIGHT'.
(Other definitions for green light that I've seen before include "something to go on" , "OK" , "Sanction" , "Given permission to proceed" , "Seal of approval" .)