You ate it here first

Oliver Peyton is waxing lyrical about cheese. Pecorino di fossa, to be exact. "It gets put in a cave for six months and it comes out with this incredibly strong flavour," he enthuses. "You go to any restaurant in Italy worth its salt and they'll produce it at the end of a meal. It's just fantastic."

He sits back, beaming. It seems that Pey- ton's discovered his foodie mojo again. It's 10 years since he opened the Deco-cavern Atlantic Bar & Grill in the formerly forlorn basement of London's Regent Palace Hotel, and during that decade he's been a prime mover in persuading wary British palates of the joys of Pacific Rim dining (at the now defunct Coast), local Italian fare (at Knights-bridge's Isola) and Gallic-inspired degustation (at Admiralty). His cool statement interiors also became prime arenas for his clubbed-out but not quite nested-up contemporaries to see and be seen in.

Now, at 41, his boyish grin may be intact, but he's redefined his priorities. "I've eaten in every restaurant that's worth the candle and loved it," he says. "But working in food does weird things to your palate. I'm only interested in eating simple stuff. I'd rather have one great thing on my plate than 20 middling." He grins. "I've gone roots up again."

What this means, in practical terms, is the strenuous sourcing of impeccable ingredients. Peyton is a rampant Italophile - his wife, Charlie, is a niece of hotelier Sir Rocco Forte - and, while he doesn't fully subscribe to the gastro-fundamentalism sweeping that country, he's a fan of the cottage-industry regionalism of Italian food production. "We're starting to see the same thing here, albeit in a tiny way," he says. "We have a small network of suppliers who are passionate about what they do, and whose stuff has an intensity of flavour you'd never find in factory-farmed produce."

Some of these discoveries will doubtless be showcased in Peyton's latest venture; Inn the Park, an all-day cafeteria opening in St James's Park in April, which will feature a huge terrace and serve proper knickerbocker glories. But in the meantime, he's asked his chefs to devise and produce a sort of fantasy menu, featuring rare or esoteric ingredients that have caught their eye.

"It's not like I asked them to go out and get a black orchid or JD Salinger's autograph," says Peyton. "I just wanted them to let their imaginations go a bit, bring an interesting dish to the table featuring produce that they're fired up by," he explains.

We repair to an Atlantic banquette and proceed to do just that. The chefs are already gathering around a selection of Italian Pomino wines that are Peyton's own contribution. "That's the only bottle in the country," he says. The first dish to arrive is a tuna proscuitto with pea shoots, onion cress, salted capers, and an apple and pear mustarda, prepared by Mark Broadbent, the bluff, hearty chef from Isola. "I found the tuna in Tus-cany," he says. "They have tons of it there. The leaves come from a British farmer called Greg Wallace. He grows interesting not-quite-the-norm things - onion cress, coriander cress. And the mustarda would normally go with cheese, but I thought it might complement the saltiness of the tuna."

"It does really linger," marvels Simon Wadham, the genial chef from Peyton's modern-British micro-brewery Mash. "It's the Mediterranean philosophy. Taking one simple ingredient and really focusing on it."

The empty plates are whisked off and replaced by the offering from Ashley Hancill, Inn the Park's youthful head chef; baby squid with a leaf salad featuring rare bronze fennel fronds. "I got the squid from Seville," says Hancill. "You can get them off British shores, but no one's exploited them. The fennel is really aniseed-y. It's from a guy called Richard Vine, who grows all our salad leaves at his * organic place near Bristol. He's intense, he pushes everything he grows to the limit."

"Awesome," declares Ben O'Donoghue, the Atlantic's amiable Melbourne-born chef and former mucker of Jamie Oliver. "They almost taste like anchovies. You could sling them in a pasta and they'd go a long way."

Next up is Wadham's Cumbrian black-pudding ravioli with poached egg and smoked haddock velouté. It looks delicate on the plate, but turns out to be deceptively robust. Wadham sings the praises of Richard Woodall, the Cumbrian farmer behind the black pudding ("he loves his pigs"), and Bill Bingham, his English egg supplier ("look at that lovely yellow yolk, totally free-range"). "I like the idea of crossing English ingredients with a Mediterranean dish," he says.

"This is really rich and grown-up," raves Broadbent. "It's got great, earthy, solid flavours. It's real comfort food."

"It's a great dish for this time of year," echoes Peyton. Judging - albeit unscientifically - from general buzz level, the black pudding is the biggest hit so far.

There's a short delay while we await O'Donoghue's whole roasted Pyrenean lamb, so the Marlboro Lights come out and the talk turns to pollock and flounder (good native fish, should be more popular), the Atkins diet (bad), supermarkets (bad, bad, bad), the ideal number of leaves in a mixed salad (three max), and the tally of great Rothschild vintages (three). The splayed and charred lamb is eventually laid ceremoniously on the table. "It's milk-fed, so you can eat all of it," declares O'Donoghue, proving his point by wolfing down the liver. The Pyrenean flocks are pretty small and the first in Europe to lamb, he explains, so they're both a delicacy and an early harbinger of spring. O'Donoghue's also done deep-fried crispy mimola artichokes from Romania. "They're like globes, but looser. Just chop it into bits," he advises. "They're delicious." I do, and they are.

Belts are loosened all round for the final offering, a chocolate caramel, hazelnut and pistachio florentine, prepared by Jane Huffer, Inn the Park's pastry chef. The chocolate is Swiss, and she's incorporated different cocoa percentages - 70 per cent for the straws, 55 for the sponge - causing everyone to ooh and aah over the clashing/complementing textures. "You know that feeling you get from great chocolate, that you're about to break out in pimples because it's so decadent?" says O'Donoghue. "That's how I feel now."

By now, we are so replete that we face the plate of rare British cheeses provided by Wadham (Coolia, Lincolnshire Poacher, Doorstone, Crockhamdale and Ragstone) with stupefaction; most of us settle for inhaling the pungent fumes. But Peyton has a final trick up his sleeve, producing one of the very pecorino di fossas that he had been extolling earlier. It has the tart, knotty ring of something that's, well, been languishing in a cave for six months - and Peyton surveys the wreckage of the table as his chefs, having polished off the last of the wine, embark on the first of many rounds of beer (good old ubiquitous Budvar, from what I can gather).

My reeling receptors are testament to the fact that Peyton has made the case for taste. "Let's do this again soon," he says, raising his glass to enthusiastic approbation.

The Atlantic Bar & Grill, tel: 020 7734 4888; Isola, tel: 020 7838 1055; Mash, tel: 0207 637 5555; and Inn the Park, www.innthepark.com