Shrewd fellow (but wasn't Billy Bunter one?) (4,3)
I believe the answer is:
wide boy
I'm afraid I can't even guess how this answer relates to the clue.
Can you help me to learn more?
(Other definitions for wide boy that I've seen before include "Tweedledum, for instance" , "Spiv" , "A rather unscrupulous person" , "petty young criminal" .)