Nicky Haslam arrives for lunch entirely swathed in shades of grey. His hair is silver. His jacket is slate. His eyes are shielded by pewter-toned reflective sunglasses. His neck is adorned with a charcoal skinny, knitted tie. He looks reassuringly expensive, as befits the 73-year-old Old Etonian great-grandson of the 7th Earl of Bessborough. But when I ask where his jacket is from, he looks at me sharply. "Zara," he barks. The shirt is "Topman, probably". His chunky Russian wedding rings are "H Samuel".
"My dread is becoming fuddy-duddy," he says. "I like looking up-to-date. I'm very interested by what you can see on the streets. It's fun feeling à la page."
Still, I expected Haslam to be more high society than high street. He made his name as an upscale interior decorator famed for his impeccable taste, and his clients – through the years – have included Princess Diana, Rod Stewart, Rupert Everett and the Dorchester hotel. He has just written a glossy coffee-table book about his own house entitled Folly de Grandeur and once penned a newspaper column called How Common, which existed purely to let lesser mortals know what was definitively below the salt (for example: "framed prints", "lying in the park" and, mystifyingly, "red wine").
Today, at Clarke's restaurant in Kensington, Haslam doesn't order red wine but sips genteelly on a rhubarb bellini. He has a taste for the sour things in life, he tells me. He "adores" capers. He drinks martinis with a pickled onion because Cole Porter once told him to. Does he like cornichons? A camp expression of surprise. "Do you even have to ask?" He says one of his earliest food memories was being asked by his nanny if he wanted "a dry dinner", which was a posh way of asking if he wanted gravy or not. "I always wanted a dry dinner," he confides, sotto voce.
He is obsessed with vulgarity and prides himself on getting things right. His new book, which he describes as "a scenic cruise" through the history and decor of his modest 16th-century royal hunting lodge in Hampshire, is littered with bons mots on all aspects of style. "There's nothing like gold to gild the lily," Haslam writes confidently. And: "Nothing is more romantic than candles outdoors in a rare breathless dusk". A caption on one page draws the reader's attention to: "[An] exquisite drawing of my Pekingese, Zephyr, as an Elizabethan lady in a ruff."
Our conversation is peppered with similar asides. He blames the death of sartorial style on the ubiquity of "blue jeans". He dismisses the wedding of the Duke and Duchess of Cambridge as having lacked "elan". Lilies are "awfully common. Too Armani for words." He can't abide it when people call Los Angeles "LA". "It drives me mad!" Haslam says, spooning a vibrant green spinach, leek and potato soup into his mouth. "It's got one of the most beautiful names – the City of Angels. Why do people do it? No one calls New York 'NY' or New Orleans 'NO'".
He says his last meal would be a cheese sandwich. What kind of cheese? "Kraft slices," he says, without hesitation. "White bread and a bit of brown sauce. There's something so satisfying about it. I'd want about four cheese slices and very thick white bread so that you can see the teeth-marks."
And then, in an unexpected turn of events, he suddenly admits that he's "mad about" Ed Miliband. "He looks like a Romantic painting!" Haslam says rapturously. "He's incredibly attractive. I adore the voice. Oh! I had a dream about him the other day, where he had long, greased-back, blue hair like a cycling helmet." I'm not sure if the Mili-crush is serious. Haslam is atypically coy about his own love life, although he admits over the course of the meal that he was sent a Valentine's card by a 46-year-old American called Joel, which he was pleased about. "He was the only person I wanted one from."
For his main course, Haslam plumps for the buffalo mozzarella and herbed goat's curd salad with pomegranate dressing. Anxious that the breast of corn-fed chicken might seem "common", I hastily follow suit.
Where does it come from, this innate belief in his own discernment? According to Haslam, it is partly a result of having contracted polio as a seven-year-old. For three years, he was holed up in a bedroom in his parents' manor home, covered in a full-body cast. His mother and her friends would pay him frequent visits. He spent his time imagining beautifully decorated rooms and pieces of furniture.
"From seven onwards, I didn't know any children," he says. "It was always grown-ups. When I went to school, I thought 'What are these horrible things who fart?' I never felt like a child."
At Eton, he indulged his taste for the dramatic by festooning his dorm with ostrich feathers. When he came out, no one was surprised. His mother, Diana, stopped in a layby while driving and asked him straight out about his sexuality. "I remember saying: 'Michelangelo was gay,'" he recalls. "She'd had four sons so she didn't mind."
With that out of the way, his life became a whirlwind of pleasure. He moved to New York in the 1960s and worked in the art department at Vogue, where he remembers the future novelist Joan Didion "weeping over her typewriter" after being let down by some man or other.
He hung out with Andy Warhol, Joan Crawford, Wallis Simpson and the Rolling Stones. He went to a succession of terrific parties and had several love affairs – in his 2009 memoir, he even claimed to have bedded Lord Snowdon, the future husband of Princess Margaret. He still enjoys a good party and throws legendary ones himself. One of his favourite guests is the American socialite Paris Hilton, who always sends a handmade thank-you card (as does Tracey Emin). He feels 27 and likes to surround himself with the young and their enthusiasms, actively encouraging everyone to leave their mobile phones on the table during dinner. "I love it," he insists. "It's fun."
Twelve years ago, he had a facelift because he was worried he was starting to look like Angela Lansbury. A dramatic reinvention followed, during which Haslam experimented with oversize parkas, ripped jeans and silver chains in an effort to ape the style of Liam Gallagher from Oasis.
"The facelift wasn't painful," he says. "You're basically swollen for nine months but no one else notices."
He breaks off to consult the dessert menu. He insists he won't have anything and then, in the same breath, orders crushed meringue with poached spring rhubarb and pistachios. When it arrives, a wobbling edifice of sugared egg white, he gives a gleeful smile. "Oh this is sinful," he declares, taking a bite.
Normally, he's careful about what he eats because he wants to maintain his impressively slight waistline. For breakfast, he has porridge with blueberries and low-calorie sweetener Splenda. "Rather a lot of Splenda," he says, shamefaced. In the evenings, he likes a bowl of Waitrose chicken soup. "I adore Waitrose, don't you?"
He's more wary about his diet after a bout of bowel cancer two years ago, though he is remarkably sanguine about his near-death experience. "I was fascinated to see what the surgeons did.
"You have to trust other people and if they're good at it, it'll be fine."
He had the tumour removed and was fitted with a colostomy bag for a few weeks, during which he went to the Oscars, wholly unperturbed. "It's a relief in a way. Not having to go to the loo is wonderful. I thought: 'At last! God has got it right.'" Still, he isn't particularly enamoured of Hollywood these days. As a young man, he accompanied Joan Crawford to the premiere of Cleopatra and he hankers after those days of undiluted glamour.
"There are no glamorous movie stars now," he sniffs. "They all try to act. It's so boring. They're not meant to act, they're meant to look wonderful."
In Haslam's world, things should look wonderful, people should be fun and life should be interesting. It's a sensible enough philosophy. He orders a black coffee, drains it and gets up to leave, draping himself in a voluminous grey scarf as he does so. "How pretty," he says about nothing in particular, and then walks out into the street.
Folly de Grandeur is published by Jacqui Small, priced £40. To order a copy for £30 with free UK p&p go to theguardian.com/bookshop
