This year, the catalyst was the appearance of a programme devoted to Little Britain, the hugely successful comedy by Matt Lucas and David Walliams. Though the series has already won two Baftas and topped the DVD sales charts in 2004, the implication in some reports was that only its admission to the South Bank pantheon could be taken as a final affadavit of excellence. And along with that came the faint mosquito-whine of "what have things come to" - never explicitly declared but implicit in the defensive quotations from Melvyn Bragg.
It is possible that he has been hit in the knee with a rubber hammer so often in these circumstances that the reflex now operates on its own, in Pavlovian connection with the duty of announcing the coming season's line-up. Did anyone accuse the programme of dumbing down this year? I don't know, since there are no hard quotes. But, if the report was accurate, he certainly defended the programme against the accusation. "It's preposterous that anyone would even think that we are dumbing down," he's quoted as saying.
Still, preposterous or not, that's what The South Bank Show press release is for now - an occasion for mild cultural regret that the pure spring of highbrow telly should have been adulterated by populism. I've even taken part in this ceremony myself - and there's something very reassuring about it. Like Midnight Mass on Christmas Eve, its pleasures are even available to people who have no intention in taking part in services for the rest of the year.
Melvyn Bragg's part in this ritual is to insist that the ingredients are the same as they were on day one. And since he might be thought to be biased in this regard, I checked up. And he's right. Season one of The South Bank Show in 1978 offered Horowitz, Satyajit Ray, Frank Auerbach and Pinter (among others) for the highbrows, Paul McCartney, Ken Dodd and a programme about the Carry On films for the populist vote.
Pick almost any season at random and the mix will be remarkably similar - that year's favourite comedian, some high-profile performers and a wedge of subjects that admirably defy the scheduling realities of a commercial channel. There is a bias for what you might call grammar-school-boy-made-good (David Hockney, Alan Bennett and Ian McKellen are all regulars) and much evidence of a cultural special relationship with the US - but there's still nothing on television that can touch it as an archive of British cultural fashion over the past quarter of a century.
The only reason problems arise, I suspect, is because the programme's single-subject approach can be suggestive of an identity of merit from week to week. And the idea that all the artists profiled have passed a famously exigent entrance exam isn't always played down by Melvyn Bragg. Walliams and Lucas, he reportedly said, "are hitting new heights of comedy" - the argument being that they are as distinguished in their field as Maxim Vengerov or Alan Bennett are in theirs. This seems to me to be a mistake - not just because I think the undoubted success of Little Britain is a touch mysterious - but because any good arts strand should occasionally make programmes about routine and mediocre work. That is, after all, what every generation for the last 3,000 years has had to live with most of the time. Excellence is a rarity, not a commonplace. And the fact that Little Britain is a bit derivative, and often downright unfunny (does anyone over the age of six really laugh at Emily the unconvincing transvestite?) doesn't make it uninteresting. It illustrates rather well how DVDs, altered watching habits (and even mobile phones) have changed the ecology of comedy. I suspect, too, that it could tell you a great deal about the enigma of the comedy catchphrase - a viral subculture that is fascinatingly indifferent to novelty or wit (or which, perhaps, renders those perishable qualities as easily tradeable as Pokemon cards).
Little Britain is not a work of "genius" - that horribly overworked comedy adjective - but it is a phenomenon. The time to grumble about The South Bank Show would be if it revealed it can't tell the difference.