The most common and most likely answer to this crossword clue is the 4 letter word LADS
I've seen this crossword clue in The Guardian
L
A
D
S
Buddy explains!

The straight part
We know that "workmates" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case workmates = lads.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 LADS mean?
LADS noun- A boy or young man.
- A Jack the lad; a boyo.
- A familiar term of address for a young man.
- A groom who works with horses (also called stable-lad).
- The penis.