A generation ago, most popular humour turned on sexual innuendo of the kind common to seaside postcards and Benny Hill, at least, outside the comedy circuit of Northern clubs, where holds were never barred: think of Bernard Manning. Today, some commentators say, humour increasingly turns on cruelty, inside the clubs and out, and even on television.
The popularity of Little Britain, with its incontinent old lady and mentally deficient man in a wheelchair, and I'm a Celebrity, Get Me Out of Here! (in last week's episode, Carol Thatcher had to eat live cockroaches, giant maggots, and a kangaroo penis), in part turns on the in-your-face disregard of restraint on the subject of who or what is a legitimate topic for humour. As a corollary, cruelty is a frequent ingredient; and the more outrageous, disgusting and un-PC the joke, the funnier it seems to be.
But is what gets described as cruelty really so? No one has ever produced a satisfactory theory of humour, but the reasons why people find something funny - different reasons for different people - must at least include the fact that it variously seems incongruous, absurd, sick, grotesque, unexpected, odd, surprising, or cruel in ways that prompt laughter by sheer reflex.
Much of what is called cruel in humour is not. Dorothy Parker's celebrated "cruel humour" was really black humour and Muriel Spark's honorary DLitt. citation at Oxford praised the "cruel humour" of one of her characters, when it was actually mordantly sarcasm.
Really cruel humour is a different thing. It is the kind that humiliates or degrades one or a few people for the amusement of many others. It is a third-person sport; only the observers find it funny, not the victims. It has to be heartless to work. A tentative or half-hearted jab at someone else's misfortune or disability, embarrassment or suffering, is just bad taste; the joke works only if the jab is a vicious one without apology or shame. As a television genre, really cruel humour was invented by the Japanese, who regard it as immensely funny to see people being put through torments and humiliations.
I'm a Celebrity imitates it, but not to the same extent. By this definition, Little Britain does not contain much, if any, cruel humour. It stands in the long and honourable tradition of absurdist and surreal comedy that began on the radio with the Goon Show and Round the Horn in the 1950s, and came of television age with Monty Python. If it differs from them in seeming to be more puerile and revolting (vomit and urine figuring so largely), that is probably because those who think so are getting older.
For genuinely cruel humour one may turn to Julia Davis's Nighty Night on BBC 3. This programme has not caused the outcry of Little Britain because it is on a less accessible channel. But there is no comparison between the two, not least because of the intelligence of Julia Davis's writing. She has a rationale for her uncompromising content, which is that if serious drama can address disability and cancer, why not comedy too.
Cruel humour shares, with cruelty to animals and children, the gratuitous, harm-and-hurt-causing callousness. Yet apart from the misery such jokes cause, the most significant thing about their presence in the media is what they say about those who laugh at them. For no joke is funny without an audience; it is funny only if its audience thinks so. For a genuinely cruel joke to be funny, its audience must have in them streak of something suitable to make it so. If British humour is indeed becoming more cruel, that last point might be the cruellest joke of all.