Gillian Reynolds

How vividly we remember when and where we hear special things on the radio, staying in a car to hear the end of a football match, being in a garden and braving hay fever not to miss a word of a play. Six Augusts ago I remember walking round the Italian Garden in Hyde Park, listening to the very first episode of That Mitchell and Webb Sound and laughing so much my glasses steamed up and I couldn't see the fountains.

They were just starting off in Channel 4's Peep Show then but had been around on the comedy scene long enough to have established their act and attracted the BBC. Radio's tiny cheques (but careful fostering) helped them to a BBC TV series. As with Dead Ringers, however, radio fans who followed them found the same jokes but with pictures, slower, still funny but not exactly fresh. Last Tuesday evening they began their fourth Radio 4 series and it was simply brilliant.

Twelve sketches, written by an encyclopaedic list of writers, lit up the air. Caesar, with a spin doctor. The iReckon, a device to enjoy the thoughts you want in the order that suits you. A reprimand to employees for using their extraterrestrial portal as a dustbin ("What must the aliens think of us?"). A parody of an interview where there's nothing to say but they won't be let go until they say what the producer wants. Parodies of TV ads and BBC formats. A look forward to 2040 and Sky BBC12. Their rapport with the studio audience is remarkable, their supporting cast is first-rate. Will I mind if all these jokes turn up again on television? Not really. If it were the other way round, TV first, I would.

Just having something to laugh at in these grim times is enough. As Rich Hall said on 4 at The Fringe, "When people are happy comedians suffer." True enough, but Radio 4 listeners have sat through enough dire comedians to know some depths of suffering for themselves.

This show, the first of two, served up four acts from this year's Edinburgh fringe, all of them established and familiar. In fact, Fred MacAulay is so familiar we're almost related. Yet his style of observational comedy is really funny (budget airlines, dogs taking over from children as sofa occupants) and his timing is flawless. That, I suppose, comes with experience.

It is mysterious how today's Twice Ken Is Plenty, the Lost Script of Kenneth Williams, ever made it to air. It goes out this morning on Radio 4 and it is, indeed, a novelty. The script turned up among the effects of the late Kenneth Williams, was bought by writer and presenter Wes Butters, is performed by two of the actors who act the parts of Kenneth Horne and Kenneth Williams in a stage version of Round the Horne. It was written by Kenneth Horne and Mollie Millest and offered, all those years ago, to the head of comedy at the time, who turned it down. Being turned down is, sometimes, a sign of something being ahead of its time. Not here. I listened to the preview disc with feelings akin to those of watching a neighbour's totally talentless child in a school concert. But judge for yourself.

Ian McDiarmid plays Dr Henry Pickerskill, retired teacher of English at a now defunct boys' public school. What he's always looked out for are oddities, the boys who didn't conform to the solid stereotype, the spirited iconoclasts, prizing them for their originality. That means, of course, the ones with a bent for junior criminality. This is his series of reports on such chaps, what happened at the school and later. It's very funny, in a sinister, sarcastic sort of way, beautifully written (by Andrew McGibbon), and brilliantly played.

Good to have them back on radio in a sketch show. Mitchell on his own as a game show host has not exactly proved a whizz though Webb, as a fine performance in a Friday Play on Radio 4 showed, is a very good actor. But together they're funnier than anything in this slot has been for months (not difficult, I grant you) because, combined, they achieve and maintain genuine momentum and their taste in scripts is first-rate. I only hope when you read this you haven't heard the same bit trailed so often you'd rather expire than listen.

This is the hallowed slot for Radio 4's topical comedy and it's a brave Controller who fills it with a brand new show. So best of luck to Fred MacAulay and his teams, competing to strike fresh sparks by rubbing together damp twiglets of the week's news. Rounds include What the Papers (don't actually) Say, Who's Who (who is the new who and why) and Apathy Attack (persuading a member of the audience to change his or her mind). Score warning: don't take it seriously. If the cricket runs over then it will be on FM only: Test Match Special will be on Radio 4 LW. No joke.

Three cheers for cricket's best team, Christopher Douglas and Andrew Nickolds, with an eve of Ashes adventure of their superb creation Dave Podmore, once an England player, later entrepreneur and after-dinner speaker now a corner shop owner, plus dogged companion Andy Hamer. This made me laugh so often and explosively while I was listening to the preview disc that a neighbour looked in to see if I was OK. It isn't just cricket that comes under their fiendishly funny scrutiny. Radio, TV, social fads and fading commentators are all there too.

Only on radio, where the listener brings the scenery, can a comedy about a small airline take off so successfully. (I'm a devoted fan of that ultra-camp TV show The High Life, but it only had one series.) This has the setting and characters from which classic sitcoms are built: a struggling business, a canny but inexperienced proprietor (Stephanie Cole), her wily chief pilot (Roger Allam), his ambitious young rival (Benedict Cumberbatch) and the good-hearted but daft son of the boss (John Finnemore, who's also the writer). It's really funny.

Here's a quick turnaround. The first transmission of Alistair Beaton's comedy serial finished only recently. Still, I don't suppose they can't often afford a cast as glittering as this so why not make the most of it? Never mind that I think it's shouty, overacted, clattering with clichés and probably originally intended for TV. See what you make of its battle for a newspaper's soul between traditional hack (Robert Lindsay), wily editor (Alex Jennings), assorted nasty females and posh Freddie (Ben Willbond) who's pretending to be a Rasta.

New sketch show. First they talk about the Depression and what effects it's having everywhere, like this team having to share a dressing room with Front Row, with "Mark Lawson's clown suit" hanging over a chair. As the show progresses many idiocies are covered: bank rescue; rebranding; social work ("a lot of the elderly are quite racist," so recruits have to be trained in how to be racist without crossing the line into the "unacceptable"). An Englishman, an Irishman, a woman and a black man provide a curiously traditional comic cast line-up.