Shumi, London W1

At the raw fish counter, chefs in samurai headscarves are slicing and whittling. There are chopsticks on the table. The menu offers a selection of lunchboxes. Welcome to London's newest Italian restaurant. In an outrageous act of GM catering, the owners of Shumi have fused two proud culinary cultures to give us "authentic Italian food, heavily influenced by the Japanese style of eating and presentation".

Occupying the dazzling 1960s building in London's clubland recently vacated by Che, Shumi is the brainchild of Jamie Barber and Geoffrey Moore, son of Sir Roger. The pair's earlier London project, Hush, is a Mayfair hellhole stuffed with more Young, Posh and Loaded than ITV's late-night schedule. Not encouraging.

But Shumi, unlike Hush, is explicitly serious about food, with a chef recruited from Conran's Sartoria, and a menu full of exciting modern-Italian dishes. My lunch guest, fish merchant-turned-author William Black, is equally serious about food. In his latest book, Al Dente, he explores Italy's history through its regional cooking. He was intrigued by Shumi's carpaccio bar which turns out Italian variations on the raw fish theme, using flavoured oils and herbs rather than wasabi and ginger.

It sits in the middle of a circular first-floor room, reached by escalator like a futuristic dining podule, or the HQ of a Bond villain (sorry, mustn't mention 007). Most tables are window-side, and at lunchtime, the shiny, all-white space is flooded with light. On the day of our visit, the only splash of colour was supplied by the orange face of the permatanned Geoffrey Moore, lounging in wraparound specs and bringing new meaning to the word "preposterous".

The staff are still struggling to master their lines, urgently spouting half-remembered guff from their training sessions. We gathered that most of the dishes on the menu are intended for sharing; that all pasta is made with rice flour to cater for the Atkins Diet brigade, and that there isn't a single Japanese ingredient on the menu. William's book is full of obscure Italian dishes, but even he was stumped by some of the terms. Our waitress was ill equipped to help. She parried any food-related query with a panicky "Would you like to speak to the chef?" and had to scurry off to check what "Shumi" meant, before returning to tell us it derived from "My Hush".

At Nobu, the meal begins with a dish of edamame - fresh, green soy beans. At Shumi, you get borlotti beans with garlic and chilli, rougher looking, but just as good to nibble. As recommended, we tried a dish from each section of the menu, starting with monkfish and tuna carpaccio. Each slice was a perfect mosaic, with a tiny jewel of deep red tuna surrounded by translucent monkfish, veined with salsa verde. Sadly, these morsels fell apart when tackled with chopsticks, and though gorgeous to look at, were too delicate to taste of much. Worse, far worse, was the pot of porcini that followed, in which any fugitive taste of the mushrooms was drowned by a honey-sweet sauce.

Having started the meal using chopsticks, we found that we were still using them for our pasta course. Given that even the Homepride flour graders are on wheat-free diets nowadays, it's canny to offer rice flour pasta. The springy texture of durum wheat is convincingly replicated, but our rigatini with cavolo nero and pancetta was dull. "If I were on a wheat-free diet, that would convince me to start eating wheat again," said William.

Of the main courses, presented on glass platters for sharing, the most tempting is probably the crispy lobster lasagne, at £30, though there are plenty of interesting (and cheaper) options. Agrodolce duck was superbly tender, with a well-balanced sweet and sour dressing and garnish of caramelised quince. William was full of praise, too, for the roasted John Dory, served on ribbons of chargrilled courgette and squash; perfectly fresh and perfectly cooked. Even the unappetising-sounding turnip tops proved to be a smart mound of dark green leaves, moulded to resemble the Japanese spinach dish, ohitashi.

"At last, they're hitting the gastronomic G-spot!" said William. But the variable quality of our meal continued with the desserts. Caramel and chocolate fondant was gorgeous, with warm caramel oozing out of its dark chocolate shell like a naughty secret. But pear and fig crostata was soggy and luke-warm.

With three glasses from the mainly Italian wine list, we racked up a bill of £125; not for nothing is Shumi housed in the Economist building. As a backdrop for the seriously glamorous, it's up there with The Sanderson and Sketch, but somehow it doesn't feel like a labour of love. And it certainly doesn't scale the gastronomic heights of Nobu. Incidentally, I checked on the web when I got home; Shumi also means "hobby" in Japanese.

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