The most common and most likely answer to this crossword clue is the 6 letter word CALAIS
I've seen this crossword clue in The Sunday Telegraph
C
A
L
A
I
S
More clues leading to the result CALAIS
- State is without a port
- French port regrettably claiming half of Channel Islands?
- Port unfortunately restricting one going under channel at first
- Bill raised sail going out to French port
- Held up in Tunisia, lacking port
- Cold unfortunately trapping one in port
- French port cold I’m afraid to say: one wrapped up
- Roughly manoeuvred sail in French port
- Caught, unfortunately, outside one Channel port
- Port with a hundred and one smuggled aboard unfortunately
Buddy explains!

The straight part
We know that "French port" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case french port = calais.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.