First of all, Reeves and Mortimer announced that they would not do another series of their hit game-show parody, Shooting Stars. Then, to a flutter of alarm at Channel Four and Hat Trick Productions, it was reported that Graham Linehan and Arthur Matthews were minded to make the third series of Father Ted, the award-winning clerical comedy, the last. Both were reported to have "axed" their respective shows - implications of sudden and untimely death which raise the large question of just what the natural lifespan of a series is.
One of the reasons these decisions (or quasi-decisions) attracted so much attention was that they were, in effect, heretical - offending against the established principal that only commissioning editors or audiences should have the power to end television life. In truth, the creators were not proposing an act of euthanasia; they were simply declaring that they would not "officiously strive to keep alive". But in doing that at a time when both programmes were in full vigour, both critically and in terms of their viewing figures, the distinction was effectively erased. Success is so elusive in this field that not to cling to it when it turns up is bound to look either self-destructive or saintly.
The most famous case of restraint - Fawlty Towers - was immediately invoked, as television's canonical example of "knowing when to stop". In truth, Fawlty Towers demonstrates nothing but the difficulty of coming up with fixed rules for comedy success. Only 12 episodes of the series were made, a decision that has usually been put down to heroic clearsightedness on the part of John Cleese. But personal circumstances probably played as much part in that decision as any artistic rigour: Cleese had just separated from his wife and writing partner, Connie Booth, and a third series would have forced on them a rather perverse intimacy. "We feel that now we are separated we ought to live that way," said Cleese at the time. "Working on these scripts means you spend more time together than the average happily married couple."
There were ideas for a third series, in fact, and Cleese's fierce quality control would almost certainly have made the finished product just as durable as the two that preceded it. What Fawlty Towers does prove is that "knowing when to stop" may be a vice rather than a virtue. In common with nearly all comedy classics, success did not come at once - only when the repeats were shown was a disappointment converted to a triumph.
Geoffrey Perkins, Head of Comedy at the BBC, testifies to the importance of staying power - "one of the things that makes a show is familiarity with the audience", he says, pointing out a number of series that only found their feet towards the end of the second batch, when they could begin to exploit the audience's knowledge of the characters. In other words, a certain amount of indifference to the evidence of failure is necessary to make any success. This can make it even more difficult for a writer to judge the precise moment at which the gradient has turned. Sitcom writers might be likened to people climbing a mountain in thick mist - will the next step take you over the top, or just a little closer to a peak you cannot see? And the truth is that early retirement is not nearly as rare as the press coverage for those two announcements might suggest - what are rare are programmes good enough to make us feel the pang of separation.
Things are different in America. There, the economy of television production, in which syndication delivers immense monetary rewards (rewards which can only be attained with large numbers of episodes) exerts a natural pressure for very long runs. American productions are also better equipped to refresh long-running shows by rotating the large team of writers who work on scripts. In this country, with its cottage-industry model of production, the fatigue of an individual writer is far more likely to make itself felt in the end result. "Two people just don't want to write 200 episodes," points out Doug Naylor, who has himself just finished the seventh series of Red Dwarf.
He also doubts that the British system can ever field enough money to persuade writers to ignore their own instincts. He himself will not sign a contract for the eighth series of Red Dwarf until he is convinced that he can go the distance with new ideas. Channel Four originally asked the writers of Father Ted for a second series of 12; they insisted on six, finally delivering eight after inspiration exceeded their cautious predictions.
But what nobody is able to predict, however acute their comic judgement, is that moment at which the affection of the audience will suddenly curdle. (The Last of the Summer Wine, easily the longest-running British comedy, shows no signs of wearying its loyal viewers, despite the fact that its tales of geriatric mischief long ago lost all capacity for surprise.)
There could be no better evidence of the difficulty of second-guessing the viewers than Only Fools and Horses, a long-running success which (officially, at least) concluded this Christmas. John Sullivan called it a day not so much because he thought the show had run out of steam (character-based comedy will always have a much greater life-span than that dependent on farcical invention), but because he thought he might not get another chance to shape an ending for his creation. The difficulties in getting the cast together for filming (a difficulty generated in part by the show's success) proved to be such that he thought he should seize the moment. The result was the biggest viewing figure in television history - an extraordinary vote of confidence that would give the most resolute writer second thoughts about retirement (there has been light-hearted talk, apparently, about a millennium reunion for the inhabitants of Nelson Mandela House). As that experience and the fuss over Father Ted demonstrates, there are only two times to kill off a comedy series - too early or too late.