Put out the bunting, crack open the beers, stand there in the kitchen smiling from ear to ear, because he’s home – our student son is home and the family is together again. And after supper, after the washing up is done, the others – his younger siblings – drift off to watch television, and he says: “Would you like to see my tattoo?”

I say, “You’re joking.”

He says, “No, I’m not.”

But still I wait. Any minute he’s going to laugh and say, “You should see your faces” because this has been a running joke for years, this idea of getting a tattoo – the hard man act, iron muscles, shaved head, Jason Statham, Ross Kemp. He’s a clever boy. Maybe during his school years he thought a tattoo would balance the geeky glory of academic achievement.

His father says, “Where?”

“On my arm,” he says, and touches his bicep through his shirt.

His lovely shoulder.

In the silence, he says, “I didn’t think you’d be this upset.”

After a while, he says, “It wasn’t just a drunken whim. I thought about it. I went to a professional. It cost £150.”

£150? I think, briefly, of all the things I could buy with £150.

“It’s just a tattoo,” he says, when the silence goes on so long that we have nearly fallen over the edge of it into a pit of black nothingness. “It’s not as if I came home and said I’d got someone pregnant.”

It seems to me, unhinged by shock, that this might have been the better option.

His father asks, “Does it hurt?”

“Yes,” I say, cutting across this male bonding. “It does. Very much.”

For three days, I can’t speak to my son. I can hardly bear to look at him. I decide this is rational. The last thing we need, I think, is an explosion of white-hot words that everyone carries around for the rest of their lives, engraved on their hearts. In any case, I’m not even sure what it is I want to say. In my mind’s eye I stand there, a bitter old woman with pursed lips wringing my black-gloved hands. He’s done the one thing that I’ve said for years, please don’t do this. It would really upset me if you did this. And now it’s happened. So there’s nothing left to say.

I know you can’t control what your children do. Why would you want to, anyway? If you controlled what they did, you’d just pass on your own rubbish tip of imperfections. You hope the next generation will be better, stronger, more generous. I know all you can do as a parent is to pack their bags and wave as you watch them go.

So I cry instead. I have a lump in my throat that stops me from eating. I feel as if someone has died. I keep thinking of his skin, his precious skin, inked like a pig carcass.

My neighbour says, “There’s a lot of it about. So many teenagers are doing it.” I stare at pictures of David Beckham with his flowery sleeves, Angelina Jolie all veins and scrawls. Tattoos are everywhere. They seem no more alternative than piercings these days. But I still don’t understand. Sam Cam with her smudgy dolphin, the heavily tattooed at Royal Ascot – these people are role models?

“My niece had doves tattooed on her breasts,” says a friend, “And her father said, you wait, in a few years’ time they’ll be vultures.”

It’s the permanence that makes me weep. As if the Joker had made face paints from acid. Your youthful passion for ever on display, like a CD of the Smiths stapled to your forehead. The British Association of Dermatologists recently surveyed just under 600 patients with visible tattoos. Nearly half of them had been inked between the ages of 18 and 25, and nearly a third of them regretted it.

I look up laser removal. Which is a possibility, I think miserably, that only works if you want a tattoo removed. And I’m not in charge here. My son is.

My husband asks, “Have you seen it yet?”

I shake my head. Like a child, I am hoping that if I keep my eyes tightly shut the whole thing will disappear.

“It’s his body,” he says gently. “His choice.”

“But what if he wants to be a lawyer?”

“A lawyer?”

“Or an accountant.”

“He’ll be wearing a suit. No one will ever know. And he doesn’t want to be a lawyer. Or an accountant.”

I know. I know.

I meet a colleague for lunch. “He knew how much it would hurt me,” I say, tears running down my face. “For years I’ve said, don’t do it. It’s there for ever, even after you’ve changed your mind about who you are and what you want to look like. You’re branded, like meat. It can damage your work prospects. It can turn people against you before you’ve even opened your mouth.”

She says, “Tell him how you feel.”

But I can’t. For a start, I know I’m being completely unreasonable. This level of grief is absurd. He’s not dying, he hasn’t killed anyone, he hasn’t volunteered to fight on behalf of a military dictatorship. But I feel as though a knife is twisting in my guts.

I get angry with myself. This is nothing but snobbery, I think – latent anxiety about the trappings of class. As if my son had deliberately turned his back on a light Victoria sponge and stuffed his face with cheap doughnuts. I am aware, too, that I associate tattoos on men with aggression, the kind of arrogant swagger that goes with vest tops, dogs on chains, broken beer glasses.

Is this what other women feel? Or perhaps, I think, with an uncomfortable lurch of realisation, just what older women feel. I stand, a lone tyrannosaurus, bellowing at a world I don’t understand.

Tattoos used to be the preserve of criminals and toffs. And sailors. In the 1850s, the corpses of seamen washed up on the coast of north Cornwall were “strangely decorated” with blue, according to Robert Hawker, the vicar of Morwenstow – initials, or drawings of anchors, flowers or religious symbols (“Our blessed Saviour on His Cross, with on the one hand His mother, and on the other St John the Evangelist”). “It is their object and intent, when they assume these signs,” says Hawker, “to secure identity for their bodies if their lives are lost at sea.”

Tattoos, then, were intensely practical, like brightly coloured smit marks on sheep.

Perhaps even then this was a fashion statement, a badge of belonging. Or just what you did after too much rum. Later, the aristocracy flirted with body art. According to the National Maritime Museum in Greenwich (they know a lot about tattoos), Edward VII had a Jerusalem cross on his arm while both his sons, the Duke of Clarence and the Duke of York (later George V), had dragon tattoos. Lady Randolph Churchill, Winston’s mum, had a snake on her wrist.

But you can do what you like if you’re rich.

On day three, still in a fog of misery, I say to him, “Shall we talk?”

We sit down with cups of coffee. I open my mouth to speak and end up crying instead. I say, “You couldn’t have done anything to hurt me more.”

He is cool and detached. He says, “I think you need to re-examine your prejudices.”

I think, but I have! I’ve done nothing else for three days! But I don’t say that because we aren’t really talking to each other. These are rehearsed lines, clever insults flung across the dispatch box. (This is what comes of not exploding in anger in the heat of the moment.)

I say, “Why couldn’t you have waited until you’d left home? Why now when you’re living here half the year?”

“It’s something I’ve been thinking about for a long time. There didn’t seem any reason to wait.”

Which makes it worse.

“I’m an adult,” he says. “I paid for it with my own money. Money I earned.”

But we’re supporting you as well, I think. As far as I know, you don’t have separate bank accounts for your various income streams. So who knows? Maybe we paid for it. “If you don’t want to see it, that’s fine,” he says. “When I’m at home, I’ll cover it up. Your house, your rules.”

In my head, I think, I thought it was your house, too.

He says, “I’m upset that you’re upset. But I’m not going to apologise.”

“I don’t want you to apologise,” I say. (A lie. Grovelling self-abasement might help.)

He says, “I’m still the same person.”

I look at him, sitting there, my 21-year-old son. I feel I’m being interviewed for a job I don’t even want. I say, “But you’re not. You’re different. I will never look at you in the same way again. It’s a visceral feeling. Maybe because I’m your mother. All those years of looking after your body – taking you to the dentist and making you drink milk and worrying about green leafy vegetables and sunscreen and cancer from mobile phones. And then you let some stranger inject ink under your skin. To me, it seems like self-mutilation. If you’d lost your arm in a car accident, I would have understood. I would have done everything to make you feel better. But this – this is desecration. And I hate it.”

We look at each other. There seems nothing left to say.

Over the next few days, my son – always covered up – talks to me as if the row had never happened. I talk to him, too, but warily. Because I’m no longer sure I know him.

And this is when I realise that all my endless self-examination was completely pointless. What I think, or don’t think, about tattoos is irrelevant. Because this is the point. Tattoos are fashionable. They may even be beautiful. (Just because I hate them doesn’t mean I’m right.) But by deciding to have a tattoo, my son took a meat cleaver to my apron strings. He may not have wanted to hurt me. I hope he didn’t. But my feelings, as he made his decision, were completely unimportant.

The stars are not wanted now: put out every one; pack up the moon and dismantle the sun.

I am redundant. And that’s a legitimate cause for grief, I think.

Tess Morgan is a pseudonym