The writing is on the wall

"Anyone entering the gallery will be subject to fictionalisation," reads the sign on the wall outside Jay Jopling's Fig 1 studio in the heart of London's Soho. It is probably the smallest art gallery you've ever seen: a single white room, with white walls and window blinds, a wooden floor, two banks of white lights - and a single exhibit. At a drawingboard, hunched forward like a man preparing to launch into a Schubert sonata, the novelist Will Self is attacking his laptop and writing a story, while gallery visitors drift in and out to watch him doing so.

WB Yeats used to meditate while composing poetry. He would concentrate on the tiny spot where the inked nib met the creamy paper, where his imagination became reified in words. Here in this gallery you can watch the same process, because the words of Self's gradually unfolding tale appear on a wall-mounted screen behind him. His fingers tap away. Plick-a-plocka-plick-plick. He appears absorbed in the narrative, oblivious to his surroundings, but he's not. You can tell because, every so often, a pungent comment about the people in the room before him appears on the screen.

WB Yeats used to meditate while composing poetry. He would concentrate on the tiny spot where the inked nib met the creamy paper, where his imagination became reified in words. Here in this gallery you can watch the same process, because the words of Self's gradually unfolding tale appear on a wall-mounted screen behind him. His fingers tap away. Plick-a-plocka-plick-plick. He appears absorbed in the narrative, oblivious to his surroundings, but he's not. You can tell because, every so often, a pungent comment about the people in the room before him appears on the screen.

The first arrivals are a TV crew from London Today, with sound-boom, lensman and bumptious interviewer with a blue suit and a tendency to yell. He explains, with grinding obviousness, that this is a case of the artist watching us watching him watching... You can see Self stiffen with dislike. "And if he writes anything nasty about me, a-ha-ha-ha," says the blue suit, "well, that's probably why they've roped him off." Self obligingly describes a film-crew fronted by a plastic mannequin - "I can see the seam running up the back of his neck". The man's neck flushes crimson. Self bashes grimly on, as unbothered as an executioner.

The story is getting under way nicely - it's a monologue about a bewildered horizontale lying in a Soho street, knocked in the gutter by a cycle rickshaw, complaining about flatulence and mercilessly guying the incurious passers-by and the people who come to inspect his recumbent frame.

Two girls in black stare at the author, clock his skinny cord jacket, skinny chinos and elastic-sided ankle-boots, stare in fascination at his wraparound sunglasses, that transform his noble physiognomy into the face of the alien in Alien; and having registered that, yep this is the most famous literary delinquent in the country, they look at the screen. "'Oooh,'" gushes the paragraph before their eyes. "'We're just here in our lunch hour, we saw it was happening and thought we'd come over and take a look'. So they gawp. They're accomplished gawpers, these two. They're even dressed in black. Could it be that they're - professional mourners?"

The two girls look at each other delightedly and giggle, then realise that even the giggle may go into the text. They say nothing. Nor does anybody else. They do not want their dull lunchtime obiter dicta to be immortalised by this bilious recording angel.

A journalist pal arrives and we say hello, breaking the silence. Whether from relief or irritation, Self hits back. I am disobligingly portrayed as "a white-haired, rubicund, leather-jacketed fellow in a waistcoat preposterously patterned with wildfowl". Fish, actually, Will - but how nice to elicit such a Dickensian flourish from the great metropolitan satirist.

Someone eating a healthy carrot sends Self into a frenzy of carrot imagery. The nasty underlip-hair of a reporter drives him to fantasise about a trip to the trichologist. Judith from Radio 4's Front Row arrives and turns up in the story as "an anaemic looking blonde in a red tunic and baggy white trousers".

Surrounded by distractions, assaulted by drilling noises, honking cars and the tramp of workmen's feet on the stairs, this is probably the worst possible setting in which to write a work of the imagination. But it's getting done, and in years to come you'll be able to tell your grandchildren, "That's me, the prat in the orange cagoule, in Chapter 3".

Self continues his extemporised tale of the city daily from 1 pm till 5pm, with a late session on Friday (4-8pm), and grand finale on Saturday at 5pm. Roll up, roll up. It is simultaneously too silly for words and quite unmissable.