The most common and most likely answer to this crossword clue is the 5 plus 9 letter word NIGEL HAWTHORNE
I've seen this crossword clue in Financial Times
N
I
G
E
L
H
A
W
T
H
O
R
N
E
More clues leading to the result NIGEL HAWTHORNE
Buddy explains!
The straight part
We know that "Knighted actor" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case knighted actor = nigel hawthorne.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.