The most common and most likely answer to this crossword clue is the 8 plus 6 letter word SQUIRREL NUTKIN
I've seen this crossword clue in The Times
S
Q
U
I
R
R
E
L
N
U
T
K
I
N
Buddy explains!
The straight part
We know that "Potter character" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case potter character = squirrel nutkin.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.