Partying with Sienna Miller? Talking tailoring with Kim Jong Un? If so, you’ll need Sir David Tang’s expertise on elite etiquette.

Thank goodness. Sir David Tang, the 62-year-old Hong Kong-born entrepreneur and the best-connected man in Britain, has written Rules for Modern Life, a “connoisseur’s survival guide” with tips on style and manners to save us all from glaring faux pas. Women should wear dresses and blouses, men suits and ties, he says. Flip-flops look better on a woman where “the foot is more slender, without the hairy shin”, but generally you should “go naked or wear shoes”. One pair of heels is enough for any woman. It’s OK for men to wear shorts — on a yacht, that is.

On he delves, into travel and etiquette and relationships and dinner parties, getting ever more brilliant and strange. Dinner party hosts should be served and start eating first. Neighbouring strangers on a flight should be ignored. Eating Cornish pasties at King’s Cross is an excellent Valentine’s date. If someone has a heart attack at dinner, everyone else should carry on. Scented candles are fine and candles generally should be “black for chicness”.

I only get rude with somebody rude — like Philip Green

Wait, what? I thought black candles were . . . “Funereal?” says Tang in his leonine, cigar-marinated growl, waving at four sable sticks on the dining table in his rooms at Albany, the exclusive apartment complex in Piccadilly, London. No, I say, just naff.

“I have black candles for two reasons,” he booms. “In support of the black race and not to be so common. Red is beyond the pale. White is very common. Green, very common, though dark green is OK. Blue is extremely naff.” Oh dear, I have worn a blue suit (and tie) rather than a black one, my default attire on the rare occasions I meet tycoons, because Tang thinks black suits are “common” and could lead to one being mistaken for a waiter or servant.

The book is hugely entertaining because, even though you may not be an international businessman who shoots with the Duke of Marlborough, parties with Sienna Miller, or holidays with Kate Moss, you can’t help measuring your life against Tang’s pronouncements. It grew out of the agony uncle column he has written for the Financial Times for the past five years. He took it on because “the discipline would put me in good stead if I ever wanted to write a book in the future”.

As he wrote in a recent column, Tang’s family was pretty much disowned by his wealthy grandfather in Hong Kong and at 13 David, speaking hardly any English, was sent to board at the Perse School in Cambridge. He is a twice-married, teetotal bon vivant, gambler and classical pianist who founded the Shanghai Tang fashion label (since sold), several private members’ clubs and restaurants, a cigar business and a lifestyle brand selling to China’s burgeoning middle class. His witty pontifications are backed up by a wide range of interests and experience.

He insists that all the queries are real, even the one about whether it is better to hang a sword over a fireplace than a TV. And he picks them all himself, even the ones that call him pretentious or a snob. “I think it is important to be loved and hated as a columnist,” he says, “so I print those letters and I trash them. It works both ways.” His responses, however puckish, are also underscored by a genuine belief that style and manners are in global decline.

“Ancient peoples regarded the importance of dressing up properly, going through rituals properly, doing things in style,” he says. “These are all things that are very basic to human nature.” Dressing well and observing patterns of politeness are signs of respect for your fellow man, he explains, and only through respectful argument and discussion rather than violence can society progress. “So it matters to civilisation as a whole that both manners and style should be kept up to speed, so we don’t forget the importance of being considerate to others.”

Tang with Tony Blair

How does this decline manifest itself? “Well, people think that at a white-tie dinner you don’t really need to go in a white tie,” he says, “but in that case you shouldn’t go. It’s a bit rude to the host. If you can afford to buy, or can borrow, a white tie, you should wear one. Not thanking people is rude. Thank-you letters are not particularly important, but it is important to acknowledge gratitude to someone who has been considerate or kind to you. People think this is all fuddy-duddy stuff, but the truth of the matter is a great deal of etiquette or standard behaviour is there to make sure people behave with good manners.”

Yet Tang admits he shouts at people, and some of his friends, such as Philip Green, are not known as the politest. “Philip Green is naturally rude,” he says. “I am unnaturally rude. I only get rude if I meet somebody rude like Philip Green. The only way to deal with bullies is to be equally rude.”

At one point, when he is praising the personal style of Kate Moss, Naomi Campbell and Eva Herzigova, I ask if they have beautiful manners to match. “They are all very, very nice to me,” he says, silkily. “Not to everybody else, I expect.” They do endlessly check their mobile phones at his dinner parties, though, which drives him wild. He possibly hates the “obsession” with mobile phones more than the smoking ban.

I ask how his 48-year-old second wife, Lucy (he has grown-up children, Edward and Victoria, with his first wife, Susanna), feels when he holds forth about women’s attire. “She couldn’t care less,” he says. “But wives, no matter how confident they are, always seek your assurance. Inside, women always like to be assured by a masculine view on sartorial matters.” He is a friend of the Prince of Wales and was also a friend of Diana, Princess of Wales, so I wonder how he reacts to the high-street wardrobe of the Duke and Duchess of Cambridge. “Diana wore jeans and was very relaxed in her style,” he replies.

However, the young royals know they have to “relate to the younger generation and they deliberately dress down and behave normally in order to do that. So you see them on Ryanair or easyJet, they wear Marks & Spencer or Topshop clothes, they are never seen at a fancy restaurant, and they are never really dressed up unless they go to a gala.” He is sure that Prince William will in due course take his duty as seriously as his father will when he succeeds the “exemplary” Queen, but worries that all this ordinary behaviour will mean some of the “mystery” and “magic” of royalty is lost.

Tang with Sienna Miller

Tang is a well-padded bear of a man, a study in shades of grey from his hair to his suit to his antique cufflinks. The decline in male peacockery he blames on the yuppies, who dispensed with ties, and the dotcom nerds, who dispensed with suits. Jeans and trainers, he sniffs, “just don’t look nice”. He approves of the “immaculate” dress sense of the late clubman Mark Birley and the “elegance” of the JCB chairman, Anthony Bamford, and cites Colonel Gaddafi and Robert Mugabe — both of whom he has lunched with — among those who got it/get it wrong.

“Mugabe, he had very bad tailors,” he says. “His shoulder pads were out there and very heavy, entirely unsuitable for a hot climate, as he should really have known. Kim Jong Un gave me the name of his tailor, who made me a suit like his — a ghastly shitty brown with a zip up the middle, short sleeves and very unflattering trousers. I’ve got the suit but can’t imagine when I would ever wear it.”

We skip through a few more of his bugbears. Marble floors in bathrooms: “Stupid.” Wine bores: “I can’t stand the way they go on ad nauseam about this claret or that claret, ‘timbre’ and aroma and ‘full bodies’.” The “iceberg basements” of the oligarch class, with their underground complexes of cinemas and gyms and bowling alleys: “Why spend so much money building rooms with no views? Stupid.”

Tang recently revealed he had the face of his “nemesis” specially printed on his lavatory paper. I thought novelty loo paper was decidedly non-U. “It’s a way of exercising contempt in quietude,” he explains. “Inevitably, my nemesis will find out, and he will know that for five years he has been the subject of ridicule.” Who is he? “He’s Belgian,” says Tang.

This shows a talent for feuding, but he clearly also has a flair for friendship. What’s the secret of turning royalty and Rolling Stones, supermodels and starchitects, Stephen Fry and Eric Schmidt into pals when they can’t have much in common apart from fame? “Osmosis,” says Tang. “To become a proper friend you have to spend time, over time, with them. You can’t rush and become an instant friend, but if you like someone you must approach it as a lifelong friendship. It’s like your affairs with your mistresses. You mustn’t treat them as transient: you have got to love them as permanent friends, so when the affair is over you remain friends. Wives as well, so when you divorce you remain friends.

“I’m incredibly lucky with all my friends because they have lived extraordinary lives. Take Mia Farrow, who must be the most intriguing woman in the world, having been married to Frank Sinatra, André Previn and Woody Allen. Anyone who is not interested in someone like that must be mad.”

He adds that some grit must be introduced to the oyster of social situations for the pearl of friendship to form. “It’s always nice to have a cross-section of people who are completely different,” he says. “So I go out of my way to invite some needling person to be around the holiday or night out, so that people can argue a bit. I like that.” A tip that, like many from David Tang’s life, may be beyond most of us, I fear.
Rules for Modern Life is published by Penguin, £12.99