A rock star's widow and an odd glimpse of celebrity

Shamefacedly, I had to realise I was only there to see the woman who married John Lennon

"Are you doing anything tonight?" my mate said. "No, nothing special," I said. "Why?" "Do you want to come and see Yoko Ono at the Tate?" "What's she doing?" "Erm - performing. I think. Putting herself on stage. Something like that."

So there we are, sitting on some fantastically uncomfortable chairs in a completely packed room with 18th-century academic history paintings on the wall. A lady from the gallery is explaining how incredibly exciting it is to have Yoko here, and how appropriate it is, given her recent concerns, that she's performing beneath John Singleton Copley - this bit rather loses me.

The crowd is mostly respectable ladies, with a scattering of mock-avant-garde figures in black, trying to look like artists - the paparazzi outside have been severely disappointed. We are clutching little torches, on which a label reading "Yoko London 2004" has been stuck over another label reading "Yoko Venice 2004." And here she comes.

Yoko looks fabulous for 70, tiny and slender in a black vest, probably very expensive cardigan and black jeans. The white braces revealed when she takes off the cardigan, however, are a mistake. She explains that she is going to explore her relationship with a chair. She walks over to the chair, looks at it, stands by it thoughtfully. She turns it on its side and lowers herself to its level. Then she proceeds to make a lot of vague, undecided gestures in its direction.

Oh God, I think, please don't let me start laughing. My jaws are clamped shut: I am thinking about anything which might prevent the uncontrollable giggles threatening to burst out. Yoko's chair is now upside down, and she is lowering herself daintily among its legs. Auschwitz, I think. Animal experimentation, I think. I can't be alone in this suffocating plight, but everyone is watching with great absorption.

Fortunately, it stops after a time, and Yoko reads out some slogans over some vaguely trancy music. This is not quite so bad. Alas, after a time, an interviewer comes on stage, and Yoko cavorts around him as he tries to ask questions, measuring him, and then explaining that with our torches we should flash the message "I Love You" - dot, dot-dot, dot-dot-dot. We all do this for a time, handkerchiefs in mouths.

And then we are into questions from the floor. Yoko has many things to tell us. We should all love each other. Water understands when you tell it that you love it and we are all made up of water. "You should be Prime Minister," a lady tells her. "How many pairs of sunglasses do you have?" someone asks. "Do you admire anyone who lived in the past?" another lady asks. "I admire everyone who ever lived," Yoko says, and nobody says, "What, Hitler?"

Someone asks about John Lennon, and Yoko talks, with some fluency, about lawyers. A brave Japanese girl apologises for her English, and asks an incomprehensible question. Yoko - it is just like one of those Beerbohm cartoons of the Young Self Meeting the Old Self - says "I'm sorry, I was busy doing something when you were talking," and doesn't answer.

After an agonising length of time, we are released from the awful chairs, and given a piece of a broken pot to take away with us. Now that hilarity is entirely safe, we strangely don't feel like it, and stand about mournfully, feeling as if we have been force-fed candy-floss. A camera crew asks us what we thought. "I thought it was lovely," I say obstinately. Blimey, I add to myself.

How do people get away with it? Of course, one has no delusions about the event. I felt like going, as everyone felt like going, in order to gaze into a deep, dark well called Celebrity. Of course, like most educated people, I rationalised it by explaining to myself that Yoko Ono was a distinguished artist in the 1960s, connected with the Fluxus group, and naturally one would want to go and see her. But in fact, rather shamefacedly, I had to realise that, like almost everyone else there, I was only there to see the woman who married John Lennon.

If she had not done that, she would now be considerably less famous than, say, Stuart Brisley, and to be honest her art was never all that terrific. No, it was vulgar gawping, and the frankly minor thrill of flashing one's torch at a perky granny-like figure, and having her flash back. Apart from that, one felt afterwards vaguely soiled by being subjected to the message that we should all love each other and then there would be no more wars, and the assurance that all human beings were immensely lucky, pronounced by one who perhaps has been more lucky than most.

I do have a serious nagging query, however. How did Yoko get started? I can see that, if you are immensely famous, you can indeed persuade people to come and watch you walk around a chair before turning it upside down. But could you ever attain celebrity by such means in the first place? Could you ever reach a position of authority just by standing on a stage and saying that if we loved each other there would be no wars, or do you have to have authority first? And if so, how do you get that authority? Just by marrying a rock star?

Altogether, a peculiar glimpse of celebrity: and I feel seriously robbed of my chance of laughing, long and raucously and heartlessly.