Captain Chervil is an Owsla officer assigned to show Bigwig around the warren when he "joins" Efrafa. Like Vervain he is something of a bully, and has severe contempt for the "lesser" Efrafans. He is very callous towards Blackavar in particular. Eventually, he was injured by Bigwig and presumably bled to death offscreen.
In the film, Chervil is voiced by Derek Griffiths. His name is also mispronounced and misspelled by some as "Sherbil".