Howard Jacobson: Rebel too strongly against seriousness and what do you end up with? Boris Johnson

He reminds me of a baby. He has the same wet, pouting lip, the same incorrigible naughtiness

There are actually people out there seriously discussing Boris Johnson becoming Prime Minister after David Cameron – a sort of Lord of the Bedchamber-in-waiting. But don't think Gordon Brown chewing on shadows for a decade in the dark hinterland cast by Tony's glitter; this is to be a suave succession of toffs. Men, at least, who have been taught manners. "After you." "No, after you." England returned to its natural legislators, right-honourables with confidence and quiffs. David, Boris, and thereafter some podgy, deeply unserious blue-eyed Fauntleroy presently fagging at Eton.

So how could so preposterous an eventuality even get as far as being canvassed? The answer is to be found in Sex and the City, handbags the size and cost of a small flat in Chelsea (at least before the fall in house prices) and those seven-inch stilettos Gwyneth Paltrow was recently seen stumbling like a lame mare all over London in.

In a word, whatever is the opposite of earnestness. Call it shine. The way the light catches a thing as opposed to what a thing in reality is. I mean no disrespect to Sex in the City by saying this. I haven't seen the film yet, but from where I live I could hear the screams when the girls teetered out on to the red carpet in Leicester Square the other day, and I enjoyed the telly series well enough. It had shine. Wit and slickness and bravura, in the service of how a thing looked. Indeed that was its brilliance – to know that how a thing looked had taken over, as a measure of value, from how a thing was.

I mean no disrespect to handbags either, nor to seven-inch stilettos, both of which interest me fetishistically. Easy for a man to say, I know. And if I were a woman I'd tell whoever came up with the idea for both to try wearing them himself, but in all likelihood he already does. There is sadism in it, without doubt. Whichever parts of a woman's body the bag doesn't damage, the shoes do. Can't be fun, being turned into a beast of burden. But speaking as a man, so long as the woman is not too manacled by fashion, so long as she can swing along, with that slightly forward-falling appearance, clip-clopping on the paving stones, mane-tossing, bag-swinging, a sheen on every inch of her, I'm for it. Clip-clop, clip-clop, and all for me, all because she wants to have my baby – for that's the dirty little disappointing secret at the heart of Sex and the City: babies – even while she's pretending she's a sexually free-wheeling feminist and has built this edifice of glitter all for her.

Ditto, if you take my meaning, Boris. Carrie, Samantha, Charlotte, Miranda, Boris. I'm not saying he wants to have my baby or that I want his – though I don't doubt there are women who do. He reminds one of a baby after all. He has the same flesh tone. The same wet, pouting lip. And is prone to the same incorrigible naughtiness. But babies apart, we like the airy insubstantiality of him. Figurewise he is not exactly a zero, but for him, too, the city is a playground.

In the course of taking on Boris, Ken Livingstone came to resemble a nun who wished she'd never given herself to God. Sadness lines appeared beneath his eyes. His skin sagged. It looked hormonal. No sheen. He had never, of course, even in his heyday, been a juicy man. He wore raincoats, kept newts, spoke through his nose, and called people "Comrade". The memory of that "Comrade" is probably what did for him. We don't want Comrade talk. Comrade talk takes all the shine off things.

Tony Blair knew that. He knew we didn't really want Labour talk either. "New Labour" was risky but it worked. Ken should have tried calling people "New Comrade". But he could never have hidden his Old Labour credentials, which meant he was only ever mayor on sufferance, partly to spite Tony whom we'd grown to hate (though not because he'd de-Laboured Labour), and partly to sort out London's traffic which we suspected needed some of the old indulgent state interference (and which, to its detriment, of course, it got).

It is no coincidence that Gordon Brown has been having hormonal problems at the same time as Ken. Also not light enough. Also no shine. There was always an air about him of a man wanting to wrest a bit of Old Labour back from Blair, and to that degree he too is the past no one any longer wants. Mrs Thatcher's great intuition was that the histrionics of socialism – its rhetoric, its vocabulary, its aesthetic – had lost its appeal to a country that no longer considered itself working class. Tony Blair's great intuition was to know that she was right. And he went one better – he doubled the shine and jumped higher to show us he was weightless. The Unbearable Lightness of Tony. Only we bore it. Anything was better than "Comrade".

The tragic vanity of Gordon Brown resides in his having thought his socialist substance amounted to more than Tony's airiness. Morally, he was right to think so. It should have amounted to more. But we don't live in a moral universe. We live now by the look of a thing. Television has changed the way we value. What doesn't slide sinuously on and off the screen might as well not exist.

So it isn't to do with class, our taking up again with popinjays. It isn't a return to an old hierarchical subservience. If anything, it's a joke at hierarchy's expense. We are showing we are no longer frightened by it. No deference this time. No one in his right mind would defer to Boris Johnson. But we like the jest against earnestness implicit in his person. Ken Livingstone was heavy with belief systems. He could barely clear his nasal passages for them. Boris believes in nothing except the absurdity of belief. Like Carrie and Samantha and Charlotte and Miranda. They know that the seriousness of life isn't really to be found in the shoes you wear. But try talking world poverty as they go clip-clopping by and you're the one that's left looking foolish.

So the burden is on seriousness now. It needs an image makeover. All the political correctness talk around race, gender and human rights over recent years was bound to let a Boris in at last. A buffoon could explode its self-righteousness and a buffoon has. We need a new vocabulary of what matters, a new language in which to express conviction; otherwise it's toffs for the foreseeable future.