The policeman carped unreasonably (6)

I believe the answer is:

redcap

'the policeman' is the definition.
(nickname for member of the Royal Military Police)

'carped unreasonably' is the wordplay.
'unreasonably' is an anagram indicator (I've seen this in other clues).
'carped' is an anagram of 'REDCAP'.

(Other definitions for redcap that I've seen before include "Hole from explosion" , "Goldfinch" , "Military policeman (slang)" , "Mil. policeman (colloq.)" , "MP" .)

I've seen this clue in the Evening Standard.

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