The most common and most likely answer to this crossword clue is the 6 plus 7 letter word PRISON OFFICER
I've seen this crossword clue in The Guardian
P
R
I
S
O
N
O
F
F
I
C
E
R
More clues leading to the result PRISON OFFICER
Buddy explains!
The straight part
We know that "Inside job" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case inside job = prison officer.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.