The others, however, are rarer specimens; the sort that Radio 3 used to call on frequently, but not often encountered on that wavelength now, where fear of prompting listeners to switch off is entrenched as the official neurosis. Both are philosophers: Philip Kitcher, who has just published a book, The Lives to Come, subtitled The Genetic Revolution and Human Possibilities, on how developments in genetics over the past 10 years have changed ideas of human identity; and John Harris, of Manchester University, author of a newly published essay on children's rights.
BBC coffee appears from Thermos flasks, croissants and pastries are offered around, but people do little but toy with them as they make introductions, swap tentative compliments, force the adrenalin to flow fast enough to create a little social warmth in the bleary haze of a Monday morning. At five to nine, Melvyn emerges from the studio, where he may have been working on his script for an hour and a half. He smiles, shakes hands and leads them into the bland studio, dominated by a broad table covered with olive-green baize. Within 10 minutes, another Start the Week is up and running.
It must be the cruellest act of scheduling the BBC has ever devised: to require of such diverse personalities, often largely indifferent or ignorant about each other's work, not merely to look interested but to participate intelligently; to transform a tough working breakfast into the sort of dinner party that people talk about for weeks afterwards - and without benefit of food or drink.
But if it's a tough task for the guests, it's barely easier on the listeners. So it ought to chasten one or two prominent people in the BBC - chasten and cause them to ask themselves some rather fundamental questions - that as the content of Start the Week has grown gradually more intellectually demanding over the eight years of Melvyn Bragg's stewardship, it has also gathered a larger and larger audience - now standing at one to one and a half million, slightly more than the far more middle-brow programmes such as Midweek, Desert Island Discs and Loose Ends which occupy the slot on other days. And not only are more people listening, more people are also responding - particularly when the content of the programme touches on abstruse scientific or philosophical questions, the BBC switchboard is blitzed with what the current producer, David Herman, calls "a happy and excited response" from listeners.
Such a state of affairs is a standing insult to those who urge the BBC to throw off the last of its old, didactic, Reithian pretensions once and for all and swim with the same tide that moves commercial radio. It suggests either that there are a lot of cussed old farts out in them thar hills, clinging for dear life to the sort of radio that they are familiar with; or alternatively, more hopefully, that there is another tide, going in another direction, which broadcasters should also be taking into account.
It was not ever thus. Once upon a time, Start the Week lived up to the breezy jauntiness of its name: it was a fast-running 70-minute concoction chaired by the arch-smoothie Richard Baker, with light features, a cookery spot, a weather update, comical calypsos sung in a fake Caribbean accent by Lance Percival, and whimsical "experiments in visual radio" in which listeners sat entranced (or switched off bemused) as Richard Baker had his feet painted, or danced with Wayne Sleep. The tone was relentlessly Baker-esque, frothy and fun without being merely vulgar, but requiring very little active exertion of the brain cells. This after all was Radio 4, ex-Home Service, radio for the nation incarnate; everybody should be kept on board, nobody should be repulsed by excessive difficulty.
The grit in the oyster was provided by the maverick humorist Kenneth Robinson, who reduced Angela Rippon to tears by attacking her book, and on another occasion caused Pamela Stephenson to pour a jug of water over him right there in the studio - not another experiment in visual radio, this, merely an urge too strong to resist. But if Robinson was outrageous and good at winding people up, there was no pretence at serious cerebral activity in his spots, either. Leave that to the deadbeats on Radio 3, with their Empire vowels, stuffed shirts and three-figure audiences.
Baker was briefly succeeded in 1987 by Russell Harty, but when Harty fell fatally ill there was an interregnum in which different anchors were tried. One of them was Melvyn Bragg, who in 1988 got the job.
He introduced radical change straight away. "I made it clear I was only interested in doing the programme if I got people I wanted to talk to," he says now. "I wanted to talk to more scientists, among other people, partly because I wanted to educate myself."
It was a sublimely egocentric criterion to bring to bear on the structuring of a radio programme. Its advantage was that if Bragg's own curiosity was gratified by the guest, his attention would be engaged and lively discussion assured. It also gave the programme a usefully blunt weapon - Bragg himself, with his own prejudices and predispositions - to wave at the marauding octopus of the book-promoting industry, always striving to wrap itself unbudgeably around the programme. (In an earlier day, Start the Week was nicknamed "Pluggers", as against the "Nutters" of Midweek and "Wankers" of Robert Robinson's late vehicle Stop the Week, which was at the same time on Fridays.) Authors could plug their wares, but they had better be pretty sure they had something intellectually substantial to plug.
And that was the other result of building Bragg's Start the Week around his own intellectual appetite. Feed him the wrong kind of fare and he could fly off the handle - not in the dubiously misogynistic manner that Kenneth Robinson was sometimes guilty of, but merely from exasperation at being fed pap or junk instead of good red meat.
Bragg's short fuse has been well known to his friends for years, but during his long and continuing run as frontman on The South Bank Show he was never anything but the perfect gentleman - erring if anything on the side of emollience. At Start the Week, for the first time he began to let his temper show. One can only speculate about the reasons: perhaps the millionaire status granted him by the floating of LWT, or the onset of middle age, impatience with his own public persona, or suppressed fury at the stubborn refusal, despite publication of novel after novel, of his literary career to properly catch fire (his 15th, a medieval doorstopper entitled Credo, is published by Sceptre next month).
This change in Bragg's demeanour went largely unremarked until 1993, when a relatively gentle dressing-down administered to the light novelist Kathy Lette caused her to run cursing and spitting to anyone who would listen. Suddenly the papers (or to be precise the Daily Mail, with broadsheets bringing up the rear), were full of Melvyn's mid-life crisis, his arrogance, his complexes, his tireless promotion of leftish causes such as theatre subsidy and constitutional reform.
Three years on, all that controversy has long died away, though he continues to fly off the handle from time to time, most recently at the expense of Tony Parsons. Meanwhile, he has stuck to his original egocentric idea for the programme - if anything rendering it more rigorous, less plugger- friendly than before. What we have now, in the words of one grudgingly admiring old Radio 3 hand, is "one of the few places on the radio these days where you can hear words like eschatological"; where, on the occasional fluke brilliant day - New Year's Day 1995, for example, when the discoverer of DNA, Francis Crick, was thrown together in the improbable company of Tom Stoppard, Salman Rushdie and Maya Angelou - the programme takes off like a rocket, all thought of plugging falls away (Stoppard flatly refused to do it), and even King Melvyn falls semi-silent as the conversation crackles around him.
It is strange to see a figure so often rubbished for being trendy leading the fight back for Reithian values at 9.05 of a Monday morning. But it's heartening, too. Start the Week is an anomaly we need.