Howard Jacobson: Bent over, pants down in front of the whole school - you can get a taste for it

"My Night of Shame with the Hamiltons" – have I told you about that? I can't imagine how it slipped my mind. 'Me, Christine and Neil – The Sordid Truth'.

We were at a literary party, doesn't matter whose. Somewhere grand. Champagne, chandeliers, canapés (don't break your heart over this), and writers – especially the initialled ones: DD This and AK That – briefly breaking out of their winter hibernations to do what writers do, compare advances, get roaring drunk, slag off the drossy times we live in, and discuss house prices in Hampstead.

So why the Hamiltons? She has produced a stocking-filler on the subject of battleaxes, and no doubt together they are working on their memoirs, but they aren't exactly writers, are they. Not what you'd call literary folk. So what were they doing here? The question was on everybody's lips, not least mine, for I am snitty about literary parties at the best of times and can never understand what half the guests are doing there. If I had my way a literary party would just be me and Saul Bellow and Salman being turned away on the stairs.

Not that I was too annoyed in this instance. It's not as though they were Mrs Thatcher and Gerald Kaufman, for God's sake, whom you also unaccountably run into at literary bashes. And they did have the decency to look out of it, Christine and Neil. He with that grey-jowled shit-eating grin of his, a beaten dog that doesn't mind who knows his disgrace now, who even wants you to see how low he's been brought and what further beatings he is prepared to take, and she comedically outraged, a woman who has woken up in a Kafka novel but because she hasn't read or finished a Kafka novel thinks it might all turn out to be rather jolly in the end, and certainly worth wearing your best slacks for.

On some sort of hole-and-corner sexual high, both of them, I thought. Public humiliation does that sometimes. Like being bent over the desk with your pants down in front of the whole school, you can acquire a taste for it.

But to return to the matter of what they were doing here, on a sexual high or not, that question so vexed the distinguished novelist I happened to be talking to, once she realised who they were, that she was left with no choice but to approach them and find out. No preliminaries. No introductions. Just "Who invited you?"

I was so shocked by the brutality of this I could scarcely breathe. Blood roared in my ears. The knowledge that I would not be able to bear such an inquisition were I ever to be subjected to it myself allied me to them. "Forgive my friend her rudeness," I wanted to say. "Welcome to literary London." But I didn't have the courage for that either. There's my shame. I left them in it. Left them to burn.

Except that they didn't. That's the difference. They are on some exalted plane of mortification, those two. They take arrows in their sides. They walk on coals. And they found the perfect answer. Who invited us? "The same person who invited you."

After which I couldn't take my eyes off them. They possessed the secret of shamelessness, the sanctified look of being roused by abasement, that complacency de la boue, such as you find, for example, among wife-swappers. I went to wife-swapping parties when I was young. I didn't have a wife but I still went to the parties.

You'll find that one or two single young men are always welcome, as long as they're good conversationalists, to help heighten the sense of danger. So I know a bit about the demeanour of swappers, how the wife always gives the room her full face, showing her teeth, how big her bite is, smudging the conventions of modesty; and how the husband, invariably uxorious, averts his gaze, appearing to be looking somewhere else, not noticing or caring, but watching all the time through snake eyes, marvellously swivelled.

Neil Hamilton has that expression off pat. Through reptilian sensors in his cheeks, he observes and approves his spunky wife. This has nothing to do with any allegations of impropriety. I'm not saying that the Hamiltons frequent sex parties, even though Christine has made it clear that if they were to – ah, that "if" – they would be in Kensington and Chelsea not Ilford. Juggling on the high-wire, that smart retort of hers.

Aristocrats have lost their heads for less. But who needs a private party, anyway, wherever it's held, when you've got the whole country watching? A fallen matron, Christine Hamilton turns her brazen eyes our way, telling us her price – so much for an interview on a couch, so much for an after-dinner speech, but no staying the whole night – and all the while her husband feigns uninterest and grows hot.

Only supposition. But I marvel at the resilience, not to say perversity, of the sexual life. Down on their luck, the Micawbers bred and bred. Enjoying the best of everything, feather beds and a fragrant wife, Jeffrey Archer couldn't wait to slum it with a tart. Every happy husband in the land shuddered when that first judge deemed such a thing impossible. They knew what His Honour affected not to: that when it comes to sex, no chain of consequences is unlikely.

Disgrace, too, then, might breed love and love breed impudicity. For it seems to be our glory, as men and women, that there's nothing we can't get off on.