"Farmer" was never an official title in this sense. It seems in any case to have died out. Mr Giles the farmer is no longer called "Farmer Giles" except by his ribald cronies in the Public Bar. Should one regret this? When and how did it dwindle? Were there others of the same sort? I feel in my bones that "Miller" may also have been used as a courtesy title. I wonder about "Squire", but that hovers between job description and social rank, so is equivocal.
Are there any job-related courtesy titles still in use? The only one I can think of at the moment is "DJ".