Of all the mechanisms for chronicling the disorientation and role reversal of political Left and Right in Britain, which has deposited those terms on the brink of redundancy, few could be more useful than the historical barometer of national rudeness that was last night's Rude Britannia, the final episode of a superb three-part series.
It used to be the case, in the aftermath of the Second World War, that those units of culture that smashed taboos were generally opposed by the Right, who felt affronted by these challenges to customary codes of decency. When the cartoonist Gerald Scarfe updated Lewis Morley's infamous picture of Christine Keeler, the call girl at the centre of the Profumo scandal, to depict a naked Harold Macmillan on the front of the Private Eye annual in 1963, the outrage came from an Establishment both conservative and Conservative.
But when, 40 years later, Little Britain was condemned for being no more than licensed chav-bashing with a dollop of misogyny on top, its opponent was an Establishment both liberal and Labour. How did we get here?
The political cartoonists of the 18th century and the bawdy music halls of the Victorian era were as nothing compared with what took off in that culturally ever-ready decade, the Sixties. Magazines such as Private Eye and Oz were in the vanguard. Then there were the comedy halls, especially in the north, where men (always men) like Bernard Manning supposedly gave voice to the prejudices of the neglected poor. Joe Orton's plays, with their rape scenes and open homosexuality, elicited screams of "Rape!" and "Filth!" in packed theatres.
It was with television that rudeness, and especially its charming twin, satire, went mainstream. Television democratises: in an age of two or three channels, everyone watched the same thing, especially since they didn't have to buy a ticket or make a journey. This made the impact of shows like Spitting Image literally phenomenal. Howls of anger greeted their arrival, but they were quenched, slowly, while the smiles of admiration broadened, eventually ceding to belly-slapping laughter.
Yet along the way, time and again, the wrong lessons were being learned. Those clamouring for censorship never grasped that satire thrives on the proximity between the satire and the satirised. In depicting the Queen as a Communist and her sister, Margaret, as a bawdy singer, Spitting Image caught the essential absurdity of both in a way no documentary could.
Nor did the forbidders grasp that the age of permissiveness they felt was opening up before them didn't have to be one where, as they feared, judgement and taste were suspended altogether. That said, the irony is that pioneers of rudeness often compliantly promoted this falsehood. Simon Donald, the co-founder of Viz, said at one point: "Comedy can't be righteous. Comedy doesn't bear analysis. Whatever makes you laugh makes you laugh, and you can't be judgemental about it."
He was exquisitely wrong. Comedy can and must bear analysis. Such analysis is called culture. Culture is that precious fund of emotional knowledge, composed of judgements big and small, that guide our sympathies. Judgement requires analysis. Rudeness and judgement are compatible.
Manning is a powerful test case. Portrayed as a hero of the poor, he in fact championed their baser instincts and so revealed his low opinion of both them and himself.
Rudeness, then, has an intrinsic virtue, realigning sensibilities, testing judgement, acting as an agent provocateur. It might offend, but then you can usually switch channel, or avoid buying a ticket in the first place. To that extent, the character behind this show was the British psyche itself, clambering up from a state of immaturity to adulthood, by rejecting the patronising assumption that we can't handle whatever knowingly disturbs us.