The National Dining Rooms, London WC2

You might think glowing reviews would be crucial to the success of Oliver Peyton's new contract catering venture at the National Gallery. Not from restaurant critics, but from art critics. A successful exhibition, after all, means a steady stream of potential customers for the restaurant and its more casual bakery/café. So when the current Americans in Paris exhibition garnered a drubbing from art critic Waldemar Januszczak, who described it as "a fourth-rate show of second-rate art by some third-rate painters", there were those who wondered if the restaurant would suffer.

Ah, but who listens to critics anyway? The bespectacled general manager of the National Dining Rooms, Marcus Etty - most recently seen running Sketch Gallery - tells me that they have had 600 covers (diners) in four hours every day.

My guess is that most of the people here would come anyway, regardless of today's exhibition, or next October's blockbuster, Velázquez; regardless, even, of the current restaurant. Predominately women in groups and elderly couples out on "a day at the gallery", they bring a genteel air to the rather sombre and unimaginative David Collins-designed dining-room.

Personally, I love being surrounded by older women. It makes me stop slouching and start using the right cutlery, as if there were one universal grandmother in the room instead of 70 individual ones. But would I bring my grandmother here, if I still had one? She'd just want a soup and a salad, or a scone and a cuppa. The likeable young chef Jesse Dunford Wood, formerly of Kensington Place, has put together a lively selection of modern British dishes, running from smoked mackerel pâté with apple and chicory, to monkfish, mullet and mussel stew, and honey-roast duck with glazed apples. But I wonder if it isn't too dinner-y.

The café seems to get closer to the point, with its savoury pies and tarts, and blissfully retro roll-call of cakes, sponges, éclairs, pies and biscuits. But the café is filled with share tables, which wouldn't have suited my gran. She would have insisted on a reservable, comfortable, low-line seat at a bare brown table of her own, in the dining room proper, with its imposing granite bar, designer light bulbs and parquetry floors. Through the windows are glimpses of Trafalgar Square and the proudly smooth, white, rounded Mark Quinn sculpture of pregnant fellow-artist, Alison Lapper. Thank heavens Gran isn't here, come to think of it.

An effort has been made to gussy up a hearty oxtail soup with bone-marrow dumplings (£7.50) by serving the meat, dumplings and vegetables first, then pouring the soup over the lot from a small jug, which would have given gran a giggle. The meat is gorgeous - tender and densely flavoured - but the broth is almost a gravy and the dumplings are glue. Much lighter is a pretty platter of beetroot-cured organic salmon (£8.50), although there is not much salmon among the small, artfully arranged orange segments, diced beetroot and delicate purple leaves.

Raw materials are excellent, as befits the British buying policy. The most expensive dish on the menu is grilled Dover sole (£23), sea-fresh, hot off the grill, presented simply with a muslin-wrapped half lemon and a separate bowl of spinach and boiled potatoes.

With only weeks of experience, the kitchen seems able to turn food out quickly. Sometimes too quickly, in fact, as I find a few things are on the undercooked side. That's OK when it's potatoes, but not so good when it's the roast chicken breast (£16.50), which is quite pink in parts. Replaced without question, take two is an unqualified success, the blond meat luscious, the carpet of potato purée voluptuous, and an accompanying "cake" of braised shredded cabbage richly satisfying. It's a natural match for a fruity, smoky Domaine Pochon Crozes-Hermitage (£26) from the compact, reasonably priced wine list.

The floor service also keeps up the pace, by way of a fleet of brown-aproned waiters who run from bossy-boots to engagingly keen. The menu lists 13 British cheeses, which is tempting for those few oldies who have not been ordered by their doctors to slow down on the stuff, and tempting fate for those who have. I go for dessert lite instead; a bowl of thin, delicate spears of pink rhubarb served with a soothing, runny custard (£6.50).

Following on from Inn the Park, the National Dining Rooms represents Oliver Peyton's further efforts to bring quality British dining to our public spaces. Full marks to the Peyton team for not dumbing-down the idea of "national dining", but a few concessions may have to be made as they go along. They seem surprised that their core market is older and/or female, with firm ideas about what it wants for lunch and how much it wants to pay for it. At the moment, the place feels like a nice lunch restaurant with a dinner menu and dinner prices: not quite Americans in Paris, but not quite Velázquez, either.

14/20

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

Sainsbury Wing, National Gallery, Trafalgar Square, London WC2, tel: 020 7747 2525 Open 10am-5.30pm Thurs-Tues; and 10am-8.30pm Wed.

Around £100 for two, including wine and service

Second helpings: More restaurants in galleries

Tate Britain Restaurant, Millbank, London SW1, tel: 020 7887 8825

Some come to the Tate for the Turners, the Hockneys and the Constables. Others come for the Latours, Musars and Gajas. Somewhere in the much-admired wine list is the perfect match for gravlax and pickled cucumber, and pot-roasted poussin.

Le Mont Urbis Centre, Cathedral Gardens, Manchester, tel: 0161 605 8282

Sitting atop Manchester's futuristic Urbis Centre, Le Mont enjoys some killer views. The restaurant is known for its modern French cooking (lobster with saffron risotto, and grilled and roasted Galloway beef rib), although long-standing chef Robert Kisby has recently departed.

McCoys at Baltic, South Shore Road, Gateshead, tel: 0191 440 4949

This classy, glassy space on top of the Baltic galleries is where well-heeled locals come for a taste of the high life. Start with French black pudding with mustard sauce, go on to seared venison, and enjoy some fabulous views on the side.