Mr Richard Corrigan is sitting at a table in his new restaurant, Daffodil Mulligan, holding a half-drunk pint of Guinness (not his, mind; he sticks to “staff tea” while on the job) over a candle, peering carefully at its illuminated contents. “Look at it,” he says. “The ruby ember, just shining in there if you look at it through a light. You’ll see a little redness. That means the yeast is very low and the pipes are clean.” He is in the middle of proving the point, with a slight smirk on his face, that his bar serves the best pint of Guinness in London.

He may have a point. Daffodil Mulligan – which opened last month in Old Street, and is already receiving positive reviews from critics such as Ms Fay Maschler – is the result of what you might call the restaurant world’s equivalent of a three-man Irish supergroup. There is, obviously, the County Meath-born Mr Corrigan, one of the best-known Irish chefs and the owner of Mayfair institution Bentley’s Oyster Bar & Grill and his eponymous restaurant Corrigan’s. There is also Mr John Nugent, founder of hospitality firm Green & Fortune. And then there is Mr Tony Gibney, owner of the famous Gibney’s pub in Malahide and a man for whom beer and stout are a very serious business indeed.

“There are people in central London saying they have a great pint and I appreciate them,” says Mr Corrigan, aiming a jovial shot at Mr Oisin Rogers of The Guinea Grill, who he fears might “take a chainsaw” to him for making such a claim. “But with Gibney and Gibney’s connections, we have the best Guinness. I do believe the pint here is a very happy pint.” So stubborn was Mr Gibney about all matters stout, that he delayed the opening of Daffodil Mulligan for three weeks until the conditions were satisfactory. “We have installed the original Guinness pipes,” says Mr Corrigan. The secret is not just the cleanliness, but the width. “We’re the only people in Britain with them. Allegedly.”

We are not here just to discuss the black stuff, however, and neither is Mr Corrigan. Daffodil Mulligan does indeed have an authentic-feeling Irish drinking den downstairs (Mr Corrigan made sure he installed a bar that was narrow enough to allow customers to shake the barman’s hand), but it is proving itself as more of a destination for eating than getting tipsy. “I can’t believe the positive response we’ve had,” says Mr Corrigan. “We have a blackboard that changes weekly, nightly. It’s printed whenever we have changes. It’s great. It’s a very free way of cooking. The ingredients come in. I just tasted some pomegranates from Sicily and I went, ‘Yeah, they’re on tomorrow with partridge.’ There’s no recipe file. There are just some great ingredients on the plate.”

It is the discussion of raw ingredients and their provenance that seems genuinely to excite Mr Corrigan. Much of what is served in Daffodil Mulligan comes from the land that surrounds his 100-acre estate Virginia Park Lodge in Co Cavan, which he took control of about seven years ago. “What we have in Ireland is our garden,” he says, talking faster the more excited he becomes. “We had the most beautiful celeriac in the other day. Carrots, beets, kales, salads. There was some lovely horseradish. Beautiful, beautiful, beautiful! When you buy in a root of horseradish, it always has flavour, but when you use your own, the intensity is a little bit more. More in the wasabi zone.” He’s not done yet. “The beef is from Tipperary. It’s fantastic. We use Peter Hannan in the north of Ireland for other meat. Then I use my English clients for partridge and mallards and things like that. We have the most beautiful people supplying us. Small artisans who have been doing it for a long time. Oysters – Mersea, Colchester’s, Carlingford’s. The amount of oysters we sold at lunch today is extraordinary. We done a couple of hundred for lunch, a couple of hundred for dinner.”

When asked what or who inspires him, Mr Corrigan does not mention star chefs or avant-garde artists. He talks of farmers, seed providers and people who spend their lives planting trees. “It has affected me to see the harmony we have created at Virginia Park Lodge,” he says. “There were no birds when I arrived seven years ago. It’s alive. And we don’t cover our fruit bushes with nets. If we don’t pick them quick enough the birds can have them.”

If there were any doubt how much of an Irish, family affair his new restaurant is, look at the larger team. His son Richie heads up front of house and his daughter Jess looks after his publicity. Mr Corrigan is also keen to pay his respects to the Irish restaurant that previously occupied his premises. Nuala was helmed by Mr Niall Davidson, who, Mr Corrigan says, is “a brilliant chef. I just think we’re an extension of all that went before. We’ve just brought the sunshine out a little bit more.” He is quick to condemn the journalist Ms Julie Burchill, whose review of Nuala for ES Magazine was called out as xenophobic by London Eater. Mr Corrigan fires off a volley of invective on the matter, before saying, “It’s outrageous to have said what she said.” Clearly, he isn’t afraid of defending himself or his homeland.

Its proprietor might occasionally get riled up, but like the “happy pint” of Guinness served at its bar, Daffodil Mulligan has joy and fun at its core. “I think hospitality is up there with great food,” says Mr Corrigan. “Boring, deadpan, serious service – who the f*** wants to eat like that any more? This is the future, I’m afraid.” Indeed, if you find yourself at Daffodil Mulligan, you may well see its owner walking around the tables speaking to customers like old friends and perhaps overegging his duties. “I like to threaten them slightly,” he says. “I told a customer the other day, ‘I cook my ribs blue.’ They said, ‘I like them medium.’ And I said, ‘Well, why don’t you try my way first?’ And guess what? They were happy.”

Make no mistake. Creating an establishment that’s this laid-back is hard work. “I’ve pounded this floor for the past three weeks and I’ll pound it for the next three months to make sure it’s right,” says Mr Corrigan. “Don’t open a restaurant and f*** off to California. I do the graft. I have the emotional scars after three weeks here. I need a f***ing psychiatrist.”