The most common and most likely answer to this crossword clue is the 7 letter word REDCAPS
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More clues leading to the result REDCAPS
Buddy explains!

The straight part
We know that "porters" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case porters = redcaps.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.
What does REDCAPS mean?
REDCAPS noun- A member of the Royal Military Police a unit in the British army.
- A porter in a US railway station.
- The European goldfinch (Carduelis carduelis).
- A type of evil goblin or imp.
- A breed of poultry.