Where those serving drinks are locked up (6,4)

I believe the answer is:

behind bars

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'are locked up' is the definition.
(I've seen this in another clue)

I can't explain the remainder of the clue.

(Other definitions for behind bars that I've seen before include "Where to find convicts" , "inside" , "Where alcohol is kept" , "In jail" , "Responsible for some music" .)

I've seen this clue in The Telegraph.

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