The most common and most likely answer to this crossword clue is the 4 plus 2 plus 5 letter word JOIE DE VIVRE
I've seen this crossword clue in The Times
J
O
I
E
D
E
V
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V
R
E
More clues leading to the result JOIE DE VIVRE
Buddy explains!
The straight part
We know that "Cross-channel transport missed if you’re late?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cross-channel transport missed if you’re late? = joie de vivre.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.