Part of underground business after revolution (6,4)

I believe the answer is:

circle line

'part of underground' is the definition.
(line on the London Underground)

'business after revolution' is the wordplay.
I cannot really see how this works, but
'business' could be 'el' (el is a kind of business) and 'el' is found in the answer.
This may be the basis of clue (or it may be nonsense).

(Another definition for circle line that I've seen is " under London".)

I've seen this clue in The Guardian.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.