The most common and most likely answer to this crossword clue is the 7 plus 6 letter word SEVILLE ORANGE
I've seen this crossword clue in The Times
S
E
V
I
L
L
E
O
R
A
N
G
E
Buddy explains!
The straight part
We know that "one may end up in jam" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one may end up in jam = seville orange.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.