Rory Wilton plays Chippy Miller in this episode and a further six. He earlier played the part of Mr Hubble in episode 5.1, Preserve the Romance (2011).
Continues the recurring various-actress herbalist character who Doc Martin's actual medical skills goes against. The first was PC Mylow's sister. Here it's Louisa's mother. This would continue until the final season with yet another actress and different character.
Louise Jameson was Tom Baker's assistant in Dr. Who; Martin Clunes's first acting job was on Dr. Who a few years later.