The most common and most likely answer to this crossword clue is the 2 plus 5 letter word GO AHEAD
I've seen this crossword clue in The Sunday Telegraph
G
O
A
H
E
A
D
Buddy explains!
The straight part
We know that "Permission" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case permission = go ahead.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does GO AHEAD mean?
GO AHEAD noun- Approval, agreement, or instruction to begin or proceed.
- Progressive; exerting leadership.
- Dashing; energetic.
- Being a score which gives the scoring team or player the lead in the game.