Four O Nine, 409 Clapham Road, London SW9

They're not making it easy to get into Four O Nine. Is it worth it?

Delightful: There is an instant conviviality and class about the Four O Nine (ANDY HOWES/PINNACLE PHOTO AGENCY)

When I was an undergraduate, there was a competition among my peers and I to discover who could best use a term from that classic text A Handlist of Rhetorical Terms without sounding like a dilettante, while at the same time extracting praise from the don. We were such chumps. I won for my use of "litotes". Aside from meaning an understatement that intensifies, and usually being expressed through a denial of the opposite (the "not un-" formula that Orwell so hated), it is an anagram of "toilets" and "T S Eliot".

It was litotes that gave the speakeasy bars of Prohibition America their outer mystery and inner charm. Soho House on Greek Street has it, too: a blank, unspectacular door, betraying no sign of the mischief or mayhem within. Understatement that intensifies.

Opposite Clapham North station in south-west London is a restaurant whose name, Four O Nine, is its street number on Clapham Road. The door is remarkably unremarkable, and the buzzer seems to demand a password; but by giving your name and time of reservation, you gain entry to a world of gastronomic delight.

Up some stairs and through a decked terrace we hit upon another door, with a short corridor leading past the kitchen and into a delightful main room, of taupe walls with public-transport prints. There is an instant conviviality and class about the place, with swivel chairs aplenty and high-end cutlery. The service is both attentive and considerate.

The menu here is short – four starters, four mains, four sides, and four desserts on a weekend lunchtime, though more at other times during the week – and changes regularly. Two excellent amuse-bouche arrive in quick succession: foie-gras parfait with black olive and chive on salted cracker; then wild smoked salmon with pickled fennel and orange-and-lime crème fraîche.

The crème fraîche returns among the starters atop a marvellous smoked aubergine soup with coriander and chilli jam, a liquidised baba ghanoush with a sweet kick that receives an approving nod from my friend. A foie gras-and-chicken liver parfait with tomato chutney is beautifully soft, though it might be better with a slightly more adventurous toast than standard white. Then there's grilled plaice fillets with peas, broad beans, fennel, cinnamon, blood orange and thyme dressing; and a buffalo mozzarella vegetarian option. This is an impressive start, given that two courses are £20, and three are £24.

Moving on to mains, my roast cod with mussels, fresh brown crab, orange, saffron, new potatoes and samphire is magnificent. A vast array of flavours clamour for attention on each plate, but it tends to work. The roast rib of beef with roast potatoes and carrot fondue comes with a Yorkshire pudding and roast wine jus, and my girlfriend's roast poussin with pancetta, spring cabbage and red grapes has "meat juices" for company. Clapham long ago reached the stage in its evolution where words such as "gravy" are thought passé, so the management here might be forgiven for bending to local custom.

The triple-cooked chips with paprika aioli (£3.50) is my favourite side-dish, and would make a brilliant bar snack if you wanted to come here just for a drink, in true speakeasy style. No substantial fault could be found, either, with the rocket and Parmesan salad, also £3.50.

For dessert, we have strawberry millefeuille and basil chantilly with cracked black pepper; a hot chocolate-and-hazelnut brownie with vanilla ice-cream; and a delicate Somerset cider, elderflower and raspberry jelly with coconut macaroon and Greek yoghurt sorbet. All are solid, though the macaroon is a little dry, and the sorbet a little bland. Best of all, however, is an outstanding chocolate fondant, which we order as a bonus hangover cure, and isn't available on the set menu.

As for the wine list – it's inexpensive, which adds greatly to the fun of the lunch.

Last year the chefs here won a Hidden Gem award from Taste London. They occupy the northern tip of a sliver of this city that, in the rapid yuppification of the past two decades, has gained surface attraction while losing inner charm. These chaps reverse that trend. Behind their unheralded door is a pleasure dome. It is understatement that intensifies.

7.5/10

Scores: 1-3 stay home and cook, 4 needs help, 5 does the job, 6 flashes of promise, 7 good, 8 special, can't wait to go back, 9-10 as good as it gets

Four O Nine, 409 Clapham Road, London SW9, tel: 020 7737 0722. Lunch Saturday and Sunday; dinner seven days a week. About £190 for four, including three bottles of wine

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Reviews extracted from 'Harden's London and UK Restaurant Guides 2011' www.hardens.com