Dinings, London W1

Nobody ever won an award for Smallest Business Growth or Tiniest Bonus Share Issue. In the West, big is beautiful, and success is measured by size.

But to the Japanese aesthete, things aren't so simple. The most sought-after master chefs in Japan tend to limit their seating to 10 or 12. My friend Tetsuya Wakuda, one of Australia's finest chefs, longs for the day when he can reduce the seats at his renowned restaurant to just six or eight. And witness Masa Takayama in New York, whose wildly popular restaurant in the Time Warner gastrocentre seats just 26 (with no menu and a spend of £150 a head, food only).

This is not an anti-Nobu/Zuma stance. I am pathetically grateful to them both for contributing such high levels of modern Japanese dining to London - something they continue to do so unwittingly, as the occasional chef peels away from the mother ship to start his own business. The latest is Tomanari Chiba, who left Nobu after nine years to open a very small restaurant in Marylebone last October. And I mean very small.

Dinings is teeny. And weeny. I bump my head twice getting to my table in the downstairs room. Only the minuscule Japanese waitress can squeeze into the space reserved for coats, and I fear that one day she could be trapped inside for hours between an astrakhan and a camelhair.

Dinings is also very, very cute, spotlessly clean and neat, and as modern as paint; a Rubik's Cube of seats, sleek wine fridges, bare brown beech tables and walls of slatted screens. One six-seat sushi bar upstairs, two small bunkers downstairs, tiny kitchen, titchy loos, and that's it.

The menu, modishly divided into "cold tapas and hot tapas", is a mix of traditional Japanese classics, post-Nobu modern Japanese dishes and some quirky detours along the way, including beef tataki with miso and jalapeno chilli, and skate wings with black bean.

For me, a Japanese restaurant will always stand or fall on the freshness of its fish. In most small restaurants, the quality is compromised by not having the buying power of the big boys. Ah, but when there is pride, respect and the telephone number of Nobu's suppliers, you can do extremely well.

Of the three cuts of tuna on the sushi list, I choose chu toro, or medium fatty tuna (£5.50 for two pieces of nigiri). It's delicate, buttery, generously sliced and on a decent slab of lightly scented rice. Also good is the unagi nigiri, or grilled freshwater eel sushi (£4.70) with its lightly smoky tang and assertive, almost meaty flavour. The wasabi is fresh, always a treat compared to the tube stuff.

Salmon sashimi salad (£5.75) is a dish I invariably find disappointing, but not here. A crisp, fresh pile of baby leaves is offset by thin slices of vibrantly orange salmon drenched in a spicy yuzu (Japanese citrus) and tomato sauce. It's manna, every bite squelching with citrussy freshness.

By now, I'm so excited about the obvious care and quality that my chopsticks are trembling. A seafood "salsa" of diced salmon, octopus, tuna and scallop strewn over layered slices of chilled bean curd (£4.75) might sound like a cheap marinara mix, but each bite has a distinct taste and texture. A fillet of Chilean sea bass (aka Patagonian toothfish) with sweet soy (£8.25), and local sea bass with a chilli sauce (£6.75) are both confident dishes, the fish lightly cooked and the sauces single-minded.

Many of the servings are small but not mean, and every dish stands alone with that wonderful clarity of purpose that makes Japanese cuisine so compelling.

I try two meaty dishes for balance, but neither the well-made grilled beef sushi rolls (£6.90), nor the grilled pork shoulder in a slightly oil-heavy tomato, lemon and yuzu sauce (£6.85) persuade me to change my allegiance to the sea.

There is room for improvement in the wine list, however, and it is hard to find wines that I think will work with such delicate food. A flat, unbalanced Kevern Walker "The Bach" Merlot from New Zealand's Hawkes Bay (£24) doesn't do much for it or me. Next time, I'll stick to beer and sake.

Dessert is not considered an essential part of the Japanese dining experience, but it sneaks under my guard, with both a black sesame crème caramel (£4.75) and a wibbly-wobbly Earl Grey pannacotta (£4.35) being well-crafted, light and uplifting rather than cloying.

The staff are rushed but charming, the prices fair, and the crowd (in this space, 30 people is a crowd) is aware and appreciative. The only downside of the size is that dish after dish gets sold out even as you are putting your order in - but this has to be seen as a positive when it is due to buying small quantities of the best and freshest, rather than bulk-buying and storing for longer.

For me, Dinings is The Perfect Small Restaurant, and my new favourite place for anything fishy, or raw or both. I just hope Chiba San makes such a success of it that he can get even smaller.

15/20

Scores 1-9 stay home and cook 10-11 needs help 12 OK 13 pleasant enough 14 good 15 very good 16 capable of greatness 17 special, can't wait to go back 18 highly honourable 19 unique and memorable 20 as good as it gets

Dinings, 22 Harcourt Street, London W1, tel: 020 7723 0666

Lunch served Monday to Friday, dinner Monday to Saturday. Around £80 for dinner for two, including wine and service

Second helpings: More former Nobu chefs

Roka 37 Charlotte Street, London W1, tel: 020 7580 6464 Kiwi head chef Nic Watt honed his Japanese skills at Nobu and at Kozue in the Park Hyatt Tokyo. This year, he rolls out the Roka robata (barbecue grill) concept in both Arizona and Macau.

Chino Latino Park Plaza Hotel, Maid Marian Way, Nottingham, tel: 0115 947 7444 Executive chef Shinji Nakamura cooked at Nobu and Tsunami before joining Chino Latino as executive chef. His contemporary Asian dishes team well with the buzzy Latin American cocktail scene.

Atami 37 Monck Street, London SW1, tel: 020 7222 2218 Formerly of Nobu and Hakkasan, Anthony Sousa Tam now brings his slick take on modern Japanese to Westminster, where the pin-striped brigade tuck into new-style sashimi and foie gras chawan mushi.