The most common and most likely answer to this crossword clue is the 10 plus 3 letter word DIPLOMATIC BAG
I've seen this crossword clue in The Guardian
D
I
P
L
O
M
A
T
I
C
B
A
G
More clues leading to the result DIPLOMATIC BAG
- Holder of secure government post abroad
- No one should meddle with this internationally sensitive case
- Controversial topic: bad mail and good mail unchecked in here
- Big capital MOD spent? It avoids normal inspection
- Admit police mostly represented talk about official case
- One might pass through customs in Germany chewing a Big Mac with pilot
Buddy explains!
The straight part
We know that "One might pass through customs" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one might pass through customs = diplomatic bag.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.