The most common and most likely answer to this crossword clue is the 3 plus 9 letter word TAX AVOIDANCE
I've seen this crossword clue in The Times
T
A
X
A
V
O
I
D
A
N
C
E
More clues leading to the result TAX AVOIDANCE
Buddy explains!

The straight part
We know that "a dereliction of duty?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a dereliction of duty? = tax avoidance.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.