It's the stuff of a publicist's nightmares. Your client opens a plush new restaurant, serving poshed-up rustic food, in one of Mayfair's grandest streets. Then, weeks before the launch, a group of teenage anarchists moves into the mansion over the road, rigs up a giant black flag and tells the press they're feeding themselves by rummaging in local bins.

Incredibly, this rich vein of material for satirically minded critics has remained largely untapped. Early visitors to Corrigan's Mayfair have been much too busy salivating over the food to bother too much about those neighbours from hell.

He's an admired figure, is the owner, Richard Corrigan; a larger-than-life Irish chef whose progress to this exalted address owes more to tortoise than hare (only the latter appears on his new menu; saddle of, with chestnut and bread stuffing).

Over the past decade or so he has created a beautiful restaurant, The Lindsay House in Soho, lovingly reinvented Bentley's Oyster Bar and Grill, done some consultancy and a little bit of telly; not spreading himself too thin, but sticking with things and doing them properly.

And never more properly than at Corrigan's, which is miraculously good. The long menu of imaginative British dishes, with the occasional Continental twist, abounds with game, wild fish and seasonal ingredients. One read and you're inclined to rush over and start rooting through the bins yourself. Linguine with red wine, pecorino and bone marrow; smoked eel risotto; game suet pudding; beef on the bone with snails and garlic butter; mallard à l'orange; grouse pie. Man the barricades, we're storming the place ...

The friendly young woman on reception made a little joke about the squat as she took our coats, setting the relaxed tone that characterises Corrigan's, and sets it apart from comparable high-end restaurants.

Waiterly fluffing and folderol is kept to a minimum, with bread basket and wine bottle left on the table for diners to help themselves. The smallish dining room, which glows in low, golden light like a copper kettle, feels nostalgic and clubbish. Quirky, fantastical touches – feathered lampshades perching on spindly duck legs and stag heads jutting from ice buckets – reference the hunting lodge without blasting at the theme with both barrels.

Game is clearly the speciality of the house, and a starter of game salad was a great introduction – slender, tender slices of pheasant, partridge and grouse, served warm and partnered with a tinglingly expansive romesco sauce. Another Corrigan speciality – transferred, along with head chef Chris McGowan, from The Lindsay House – are crubeens, crisp croquettes of shredded pigs' trotter, truly light on their feet, here draped with Jabugo ham and served with beetroot relish.

Daube of pork, with turnips and spiced apricots, had a tagine-like richness, and the casserole was left on the table so the dark gravy could be mopped up with nutmeg-scented creamed potato. If all this sounds a little heavy, the kitchen proved itself equally adept with fish dishes; plaice fillets sandwiched around brown shrimp and fried in an almond crumb were fluffily light and utterly plaice-y (technical term).

From a dessert list that offers the intriguing sounding lime and cheese soufflé, quince tart was what you'd have to call an eating pudding rather than one to feast your eyes on, chunky of fruit but delectably light of pastry, and partnered with Sauternes ice cream.

Corrigan's may not offer waves of unadvertised mini-dishes between courses, but there's a generosity about the place that comes across both in the size of the portions, and the approach of the wine list, which favours small, biodynamic growers and is full of reasonably priced alternatives to the usual suspects.

The sommelier steered us, in the most engaging and non-shaming way, towards an Austrian red – a fruity St Laurent Reserve (£42) – which worked brilliantly across the meal. Also welcome was his recommendation of a glass of spicy chianti rufina rather than port to accompany a plate of British and Irish cheeses.

The Saturday-night crowd was more mixed than you might expect from the Mayfair address. The restaurant is adjacent to, but independent of the Grosvenor House Hotel, and a hubbub of noise from a party next door added to an atmosphere already relaxed by the presence of a large family group celebrating a birthday.

After a couple of high-profile, but underwhelming, recent modern British openings it's great to report that Corrigan's has got it so right. Great ingredients, imaginatively cooked, with the perfect balance of simplicity and cheffy artistry and no trace of the cultural cringe. Truly, when it comes to flying the flag, I know which side of the street I'd rather be on.

Corrigan's Mayfair, 28 Upper Grosvenor Street, London W1 (020-7499 9943)

Food 4 stars
Ambience 4 stars
Service 5 stars

Around £40 a head before wine and service

Tipping policy: "Service charge is 12.5 per cent discretionary, and the staff receive 100 per cent of the service charge; all tips go to the staff"