Sake no Hana, 23 St James's Street, London

So this is how it must have felt to be around during the last days of the Roman Empire. Sipping Krug champagne (£30 a glass) and nibbling lotus root tempura (£2 a bite) at a sunken table high over St James's (squillions of pounds per square metre) while one's stockinged feet are warmed by an under-table heating system. Not a feat of time travel, but one of income travel; this is how London's rich and fabulous will be taking their Oriental food in 2008, with the opening of Sake no Hana, already established in fashionable circles as "the new Nobu".

The owner, a Russian billionaire whose previous investments have included Geri Halliwell, has recruited the restaurateur Alan Yau to front up his modern Japanese restaurant, in a partnership of big bucks and creative brilliance unrivalled since Abramovich hired Mourinho. The venue, a Sixties landmark built for The Economist, stubbornly refused to surrender to the last two high-end restaurants that opened and closed there in short order.

The food is inspired by rustic dishes, and ranges far wider than most Japanese menus tend to. With Wagamama, Alan Yau democratised Japanese food; here, he is working in the opposite direction, presenting home-style dishes in tiny portions for the well-heeled and carb-averse.

Just how well-heeled diners are is on literal display; shoes must be removed before you're allowed to slip into your tatami-lined conversation pit. God forbid you should be wearing Office knock-offs; they'll stand sentry by your table, letting you down, for the rest of the evening. The entrance is via escalators, which glide up through halls of lacquered black and gold reminiscent of the heyday of Biba. Upstairs, there's an abrupt change of style, as shiny black yields to golden wood, bamboo, natural textiles, and a petrified forest of giant Jenga rods suspended from the high ceiling. It's all beautiful, in an other-worldly sort of way; like being in an artist's impression of a finished building rather than the real world.

The menu, too, causes a temporary disorientation, divided as it is into a succession of unfamiliar sections. But as there appears to be at least three attentive staff per diner, it's not hard to steer a course from light dishes and sashimi, through tempura and sushi, to braised dishes and the noodles and rice with which Japanese meals traditionally end.

We chose a couple from each section, and our stab-in-the-dark ordering technique threw up some inspired dishes, notably an appetiser of warm, silky aubergine flesh dressed with sesame and bonito flakes, and from the grill menu, a miso-sweet slice of Chilean seabass which had a rich, glutinous texture that recalled Nobu's famous black cod. From a tempura list that charges per single item, alerting you to the fact that you are paying £1.50 for a stalk of asparagus, we chose lotus root and courgette flower, and were rather more aware of the taste of the batter than we should have been.

Sashimi and sushi, created in a self-contained sushi bar downstairs, were great, though our sampling of botan ebi (raw prawn) revealed that there's a good reason why prawn is usually served cooked. And another warning: on no account ever go near ginkgo nuts, unless armed with a large hammer; they look like pale olives, and taste like washing-up water.

Overall though, this is cooking of a very high quality, and like Yau's brilliant Hakkasan, the menu no doubt continues to yield its pleasures gradually, through exploration and experimentation. Though it seems to be food for sharing, many of the dishes are barely big enough for one; perhaps going out with Geri Halliwell gives a chap a funny idea about portion control. But weirdly, our meal climaxed with an enormous pot-sticker of a main course, a slow-cooked stew of black leg chicken, sugar snaps and carrots that could easily have fed four. It involved a great deal of fossicking around by our waitress, who reverently offered up the tastiest slivers of meat for our delectation. That she was obliged to take her shoes off and perch tableside to do so only increased our feeling of pampered discomfort.

Uniquely for an expensive London restaurant, Sake No Hana doesn't have a wine list; instead, the sommelier guides you through an exhaustive menu of sakes, many of which cost upward of £100. If it all sounds a bit decadent, that's because, as you're probably picking up, this is a restaurant that's not really aimed at the general dining public. This is somewhere to bring a visiting Hollywood star, or to squire a supermodel, and only Premiership footballers would use it as a venue for a convivial dinner with mates.

It's conceivable that if you ordered carefully, you could get out for less than £50 a head, but that isn't the point of Sake No Hana. Like the clubs of St James's that it looks out over, it is designed for a breed apart. And unless you have the backing of your own personal Russian oligarch, that probably doesn't include you.

Sake no Hana, 23 St James's Street, London SW1 (020-7925 8988)

Food
Ambience
Service

Dinner for two with sake around £180

Side Orders: Turning Japanese

By Madeleine Lim

Zuma

At around £80 per head without drinks, it's expensive – but you're paying for the celebrity-driven atmosphere as well as the excellent modern Japanese food; try the beef tataki and spider crab sushi rolls.

5 Raphael St, London, SW7(020-7584 1010)

Umu

Meltingly fresh sashimi and silky Wagyu beef with wasabi are two of the specialities in this elegant Michelinstarred Japanese. Prices are sky-high; a more painless option is a set lunch from £22.

14-16 Bruton Place, London W1 (020-7499 8881)

Nobu

You'll need to book ahead to get a table at what is still considered by many to be London's most glamorous restaurant. Try the black cod in miso, beef with teriyaki sauce and rock shrimp tempura.

Metropolitan Hotel, 19 Old Park Lane, London W1(020-7447 4747)

Bincho Yakitori

This new Japanese specialises in tapas-style flame-grilled dishes and skewered meats. Amazing views across the Thames and good prices, too – around £25 per head.

Oxo Tower Wharf, Bargehouse Street, London SE1 (020-7803 0858)