In summer 1795, George Canning, future prime minister, records some tantalising news in his diary. "Mr Gillray has been much solicited to publish a caricature of me and intends doing so!" he swanks. A month passes without the promised glory. He admits to concern. By Christmas, there is still no image.
In the end, Canning waits an agonising year – furtively checking the print shops – for the negligible honour of appearing as a corpse in Gillray's Promised Horrors of the French Invasion. But by then vanity has devoured him. You might say he has already turned into a Gillray caricature.
Life imitating art: that is one measure of a caricaturist's genius. Another is the masochism of his victims – the celebrity buying her own Spitting Image puppet, the politician hoping to appear in a Steve Bell cartoon. In which respect, as in so many others, Gillray still reigns supreme, this artist who could mock the Queen as a syphilitic crone with wizened dugs bared, talons clawing at the prime minister's crotch, and still find eager patrons at the palace.
You will not see this devastating image in Rude Britannia at Tate Britain. Perhaps the curators did not find it comic. Their Gillray is the schoolbook satirist, the man who drew Pitt and Napoleon carving up the plum pudding of the world and that dangerous revolutionary Charles James Fox with no trousers (sans-culottes? Remember?) Likewise, their Hogarth is the author of those history lesson classics, Gin Lane and Marriage à-la-Mode.
But if that sounds too regular, too tame, not funny enough, the curators then go mad in the other direction. An entire gallery, lined with blushing red wallpaper, is given over to cocks. Here they are – ha ha – in the hands of Sarah Lucas, Grayson Perry and Beryl Cook's fat ladies, to name an assorted few. Aubrey Beardsley's illustrations to Lysistrata, with all their whiplash elegance, appear alongside a cartoon of Rupert the Bear penetrating Mary Whitehouse while the Pope looks on. Lord knows what mirthless debates must have occurred, how the organisers ever managed to limit their scope.
However they did it, the result is surprisingly poor. This show is all over the place. But perhaps it could not have been otherwise. Any exhibition that includes everything from toby jugs to the highly original humour of Max Beerbohm in the last century and David Shrigley in this, that runs all the way from Gillray to Donald McGill's jolly seaside postcards without any obvious change of tone, is clearly suffering from too many conflicting ambitions. And any show of comic art that barely includes any paintings after Hogarth has a peculiar sense of humour and art.
Rude Britannia aims to give a complete history of the genre, starting with some of the most academic and least humorous of prints – Dutch allegories of British politics, Oliver Cromwell crowning himself king (what else?) – and ending with some of the flattest works of contemporary art you could find. In between, you have a sense of the curators trudging through the archives to find the earliest cartoon strip, the first ass-kissing image, the original Napoleon chamber pot offering the owner a chance to pee on Boney's head.
Then the show wants to identify a distinct and robust strain in British art, starting with Hogarth. This is perfectly fair, though I suspect it wants to go further and present Hogarth as the father of British art per se. To achieve either, it has to be historic, scholarly, comprehensive – this is Tate Britain – yet it has sections on the lewd and crude so as not to appear embarrassingly swottish. And at the same time, it wants to be funny.
To this end, one of the best and yet most counterproductive tactics is to involve the Viz creators throughout the show. They have put together a special issue of the magazine, blown up to the size of a billboard, sending up the art world and all its denizens. Look out, in particular, for the letters page with its very acute send-up of one A Gormley.
They have also been commissioned to write the flannel panels for the 18th-century room. The paintings and prints here have been defanged by time. Who knows the significance of the bosomy woman showing off a mouthful of surprisingly sparkly teeth (porcelain gnashers: made in France and thus instantly political) without explanatory context. Step forward Roger Mellie (The Man on the Telly), foul-mouthed lush and notorious misogynist, plus his straight man, producer Tom.
At which point, you might as well draw a veil over the historic works, so completely are they upstaged by Viz's storyboards with their gleeful contemporary humour.
And the point is made by the comedian Harry Hill in the catalogue: you don't need to know about art to love it, whereas you may need to know something about John Major's career as an accountant and politician to understand why Steve Bell's immortal underpants are funny. Bell's apocalypse of Major's pants going up in flames on the Thames, with its nod to Turner's famous painting of the House of Commons on fire, is one of the most searing works in this show: a stunning conceit, a marvellous execution. Not incidentally, it is disappointing to have so little of Bell – or Ronald Searle, or Beerbohm, or HM Bateman, come to that – in this show.
For this is essentially a portrait of the graphic tradition. It has no room for a mordantly comic painting like Gainsborough's Mr and Mrs Andrews, he with his self-satisfied smirk, she with her sly, St Trinian's expression, posted like gatekeepers in front of the view that they own. Is it funny, is it art?; the two questions anyone might ask about the works in Rude Britannia both seem to be answered in the affirmative by this canvas. Perhaps they couldn't borrow it. Still, it is just up the road in the National Gallery.
In some senses, the exhibition fails in the way that humour itself can fail. It lacks surprise. It lacks brevity. It requires extensive explanation of context and detail. You had to be there, to use that deflating phrase. And artists, unlike comedians, do not have to be funny to make a living in any case. A punchline is never required.
But what Rude Britannia does present with real clarity is the outline of a particular tradition in British art. It is an art of the body, of corpulence and skinniness, flatulence and dropsy, of comic priggishness and irrepressible lust. It is the enormously billowing woman and the little half-pint man, the scrawny neck and the woodpecker drill of a nose. It is greed and lechery and gaping cakeholes, bulging trousers and breasts like buttocks, Bash Street shins and unfeasible genitals. It is Leo Baxendale's Beano, it is Phiz and Viz, it is there in modern masters such as Gerald Scarfe, Steve Bell and Martin Rowson. You can see it in Hogarth, of course. You can even see it in William Blake if you look. But, to me, it all goes back to Pitt and Fox and the caustic genius of James Gillray, most inventive of British comic artists.
