Deputy who upset some columnists (5)

I believe the answer is:

locum

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'deputy' is the definition.
(both can mean a substitute or stand-in)

I don't understand the remainder of the clue.

(Other definitions for locum that I've seen before include "Temporary replacement doctor" , "Temporary deputy for doctor" , "Professional who stands in for another" , "Doctor's deputy" , "Physician's stand-in" .)

I've seen this clue in the Evening Standard.

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