The most common and most likely answer to this crossword clue is the 4 plus 2 plus 6 letter word COME ON STREAM
I've seen this crossword clue in The Guardian
C
O
M
E
O
N
S
T
R
E
A
M
Buddy explains!
The straight part
We know that "start working regularly" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case start working regularly = come on stream.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.