On the conveyor belt tonight...

Ian Fleming introduced me to sushi. After seeing Dr No when it came out in 1963, I devoured every James Bond novel within weeks. Besotted with this exotic, dangerous world, I heard about (and bought) a new non-fiction book of Fleming's called Thrilling Cities. Fleming describes food precisely and enticingly, and two of the foods in Thrilling Cities were called sushi and sashimi. They were raw fish, that much I understood; just as I understood (from You Only Live Twice) that Commander Bond ate a Japanese meal starring a lobster that tried to crawl away.

Ian Fleming introduced me to sushi. After seeing Dr No when it came out in 1963, I devoured every James Bond novel within weeks. Besotted with this exotic, dangerous world, I heard about (and bought) a new non-fiction book of Fleming's called Thrilling Cities. Fleming describes food precisely and enticingly, and two of the foods in Thrilling Cities were called sushi and sashimi. They were raw fish, that much I understood; just as I understood (from You Only Live Twice) that Commander Bond ate a Japanese meal starring a lobster that tried to crawl away.

As a gastronomically adventurous tyke in New York, where foods of all kinds have always been possible, I begged my parents to take me to a restaurant where I could eat raw fish. They did. I loved it. When I told my friends, they thought I was a pervert. Nowadays, as a wave of raw fish washes over Britain, sushi perverts are people who don't like the stuff.

Tesco claims to sell an astonishing seven million pounds a week. Sainsbury's sells more sushi than cheese rolls. Even Asda is being told by market researchers that its customers want sushi. What used to be an exotic luxury has become commonplace. With a flick of the chopsticks, we believe we've bought some of the benefits of the Japanese diet, enabling us in a single lunch hour to compensate for a lifetime of less healthy Western eating habits. The bandwagon is rolling.

And it rolls increasingly on a conveyor belt, as kaiten sushi. These conveyor-belt restaurants are considered rather downmarket in Japan, but in the UK, slow-mo salmon is all the rage.

Moshi Moshi Sushi, the original kaiten operation (founded in 1994), has three restaurants in London, one opening in Brighton, and unspecified plans for further openings still. Even more successful is Yo! Sushi, where the conveyor belts team up with robotic drinks dispensers and video screens to supply high-tech entertainment. Yo! has eight restaurants, with five more planned and ambitions for international expansion.

I should be pleased about the sushi craze; instead I'm sorry that so much of what the new sushi-philes are eating is far removed from the real thing. Part of the pleasure of eating sushi is, as the Yo! gang have spotted, a theatrical pleasure. In a sushi bar, however, the theatre is provided by a chef. He sways or rocks, as if in a trance, while moulding the rice lozenges; he addresses the slab of fish like a sculptor with a block of marble; he slices and assembles with deft precision; he presents it with a graceful bow. You feel honoured.

People who eat supermarket sushi at their desks, bowing resentfully before their PC, miss the personal element. And they miss, more importantly, the superlative quality of sushi made on the spot. Imagine what you'd think of pizza, hamburgers or lasagne if youknew them only from their mass-market incarnations.

Something is lost when a gastronomic art form transmogrifies into a product for mass consumption, and sushi comes as close any food to the status of art. It occupies a world of rituals, shrouded in myth and legend. It demands exacting standards in selection, preparation and serving of fish, rice and garnishes. And the people who make it have, traditionally, spent years learning how. Even so, I've known amateurs who made delicious sushi without any training. And given the nose-bleed prices charged at the priciest Japanese restaurants, who, except a connoisseur, knows how much of the cost is for the mystique as much as the skill?

But whenever I survey today's mass-produced, long-shelf-life sushi, I think of Ishi, the only sushi chef I have known personally. Ishi told me you have to eat sushi or sashimi at the bar, because the fish starts losing flavour the instant it's sliced. And as much as I've enjoyed sushi from low-priced joints, none has delivered the quiveringly fresh flavours dished out by Ishi and his peers.

With these doubts in mind, I called Philip Karhu, sales and marketing manager for Noto Catering. Noto makes around 50,000 pieces of sushi a day for clients including Pret A Manger, Harrods and Selfridges. For mass-produced sushi, they're just about the tops. Their operations are headed by a master sushi chef called Mr Shimo.

"There's no doubt that sushi is best served straight across the counter," Mr Karhu agreed. But Noto has adapted, tailoring ingredients and handling to the lag between production and consumption. It's a compromise: a good product at a price ordinary mortals can pay. But there's only so far they'll go. They refused to supply a supermarket with sushi which would sell at the lowest possible price and keep well beyond the 24 hours which Noto regard as the maximum. Mr Karhu sees advantages in the dissemination of sushi through supermarkets. "The quality may be marginal in some cases, but as it increases awareness, consumers may make a step up."

I'm not so sure. My experiences of real mass-market sushi suggest it looks right and tastes boring. That gorgeous blossoming of tastes and textures just doesn't happen. True, top-notch sushi costs, and many consumers simply want cheap food. They're expecting the impossible. What they're getting, in some cases, is McSushi.

Sushi is meant to be a sensuous thrill, an aesthetic experience, a demonstration that less is indeed more. If you buy it on the way home, and eat it watching Big Brother rather than from chef Ishi, it's a cut-price short-cut. You're simply filling your stomach with raw fish and cold rice. Is that what sushi should be? I'm not convinced.