Since I began this column I have been unstinting in my support of Radio 4. Still, nothing lasts for ever, does it? This past week everything that I listened to had me retching into the bread bin, a reminder that when the station reverts to type, its middle-class smugness quite takes the breath away.

First up was a new quiz show called Where in the World (Wednesday, 1.30pm). Radio 4 is obsessed with quizzes; like some unfashionable public house, it believes they will pack in the punters. For this ploy to be successful, however, the questions must genuinely tug at the mustier recesses of the brain, and the "celebrity" contestants must be clever and funny without ever appearing to show off or, worse, name-drop. This one failed on both counts. I was stirring a pan of porridge while it was on, and the oats in question - grey, lumpy, familiar as old wood-chip wallpaper - were far more interesting than anything that Chris Bonington said.

Where in the World is a fancy geography quiz - or, as the producers have it, "a journey of discovery" around the "planet we call home". Here, merely knowing the capitals of the world will get you nowhere; remembering that Vasco da Gama sailed to India in 1498, on the other hand, will have you cruising to victory. The show is presented by John Simpson, a fine reporter who is fatally hampered in this instance by both his grand manner ("I used to know Hemingway's third wife," he said at one point, launching into a wincingly bad impression of Martha Gellhorn) and his lack of a sense of humour (in the same way

as you gather a politician is trying to make a joke,

your cue comes a full four seconds later, when the lackeys dutifully begin chuckling). Why was he chosen for this job? Isn't there some conflict out there that he should be covering instead?

To be fair, Simpson gets no help from his contestants, who are required to trot out their own travellers' tales in the course of answering his questions. And here's the rub. The makers of this programme have entirely forgotten that there is nothing on earth so dreary as hearing about someone else's holiday. Bonington was joined by the writer Simon Brett and Rachel Holmes, who used to run Amazon UK. Brett was so hesitant I wondered if he was not boring himself; Holmes squeaked that she longs to visit Valencia because she likes gazpacho. Bonington, meanwhile, shared his love of military history. He was so eager to talk about General Gordon that he continued droning on about him even after Simpson said that the correct answer to the question had to do with the Alamo. I bet the Bexhill-on-Sea Rotarians put on a better show than this.

I only caught - forgive the pun - the first part of Human Hosts (Monday-Friday, 3.45pm), in which parasites told "their own stories", but that was enough to tell me that someone at Radio 4 obviously imagines that its listeners want nothing more than to revisit the dire schools education television programmes we were forced to watch back in about 1979. Each day a different actor played a different parasite. On Monday Tony Robinson was a pinworm: an adenoidal, smart-alec pinworm who spoke with his mouth full and, in order to explain to us thickos how his kind are passed from one human being to another, said things like: "Scratch your bum, suck your thumb and . . . bingo!" Here's a quiz question for the person who commissioned this: How dumb do you think we are?