Somewhat retired MP, or chief whip (4)
I believe the answer is:
crop
'whip' is the definition.
(crop can mean a whip)
'somewhat retired mp or chief' is the wordplay.
'retired' says the letters should be written backwards.
'somewhat' indicates a hidden word.
'porc' is hidden within 'mp or chief'.
'porc' reversed gives 'CROP'.
(Other definitions for crop that I've seen before include "distress, as it were" , "Trim (a photograph)" , "It's produced at harvest time" , "Hunting whip" , "Type of whip" .)