Read Giles Hattersley's interview with Uma Thurman

The paparazzi could hardly believe their luck. As the 100 guests made their way into the multimillion-pound London home of Arpad “Arki” Busson, the financier and philanthropist, to celebrate his engagement to the Hollywood A-lister Uma Thurman last week, almost everyone seemed worthy of a picture.

“It was a superglam occasion,” gushed one attendee. “Everyone was there – rock stars, supermodels, actresses, moguls and party girls. The guest list was, of course, pure social Viagra.”

The hostess, dressed simply in a long white gown, welcomed her guests with champagne and an Italian buffet. A couple of marquees had been erected in the garden for the party to spill out onto the lawn.

Liz Hurley talked to her old friend the shoe designer Patrick Cox, while two knights of the business world, Sir Philip Green, of Topshop fame, and Sir David Tang, the entrepreneur from Hong Kong, held court at opposite ends of the room. Damien Hirst headed the list of artists present; Sir Elton John, the pop stars. As usual Sting and Trudie Styler were indulging in public displays of affection.

“It was great fun,” reported Uma’s father Dr Robert Thurman, a Buddhist writer and academic, who was in town to promote his latest book, Why the Dalai Lama Matters. “It seems they’ve really found something in each other and that’s truly great. That’s the key thing. It’s nothing to do with social status, money or celebrity – it’s the emotional connection between them. Though, of course, they’re both really quite good looking.”

And rich and glamorous and impossibly well-connected. Busson and Thurman are not just any old power couple. With everybody from the Dalai Lama (an old friend of Dr Thurman’s who used to stay at the family’s house) to Madonna and Guy Ritchie, Bill Clinton and Tony Blair on speed dial, and the clout to attract a guest list that made last week’s event unquestionably the party of the season, they are, at least for the moment, Britain’s superpower couple.

Every summer, a couple comes along that raises both the social and tabloid pulse. Hugh Grant and Hurley, Jude Law and Sienna Miller, Grant (again) and Jemima Khan, have all fitted the bill. A couple of years ago, Kate Moss and Pete Doherty increased the temperature with their sheer unpredictability; and last summer, following their temporary split, Prince William and Kate Middleton suddenly became a talking point again.

This year it’s the turn of “Uma and Arki” – as they are already known to the tabloids. Why the interest?

“It’s the gods at play,” said Kate Reardon, a contributing editor to Vanity Fair, the American magazine. “She is mesmerisingly beautiful, but also a good actress. He is traditionally handsome and insanely successful. What’s not to like?”

Some of us may, of course, may be envious of such qualities, but also intrigued by how the relationship functions.

“We love the idea of people huntingin pairs, working together,” said Peter York, the author and social commentator. “Posh and Becks are all about working together. We may laugh at her funny clothes, but she is the person who recognised David could become a global brand.”

A thrilling back story also raises a couple’s stock – not to mention the feeling that an exciting new relationship may not last all that long.

“There is a much greater sense of risk in two very high-profile people getting together, because there is the potential for their joining of egos also to become a competition of egos,” said Geordie Greig, editor of the society magazine Tatler.

Thus Carla Bruni’s past relationships with Mick Jagger and Eric Clapton, combined with Nicolas Sarkozy’s marital breakdown, made the French presidential whirlwind romance all the more intoxicating for onlookers.

Thurman and Busson are no different. At 38, Thurman, the American star of Dangerous Liaisons, Pulp Fiction, the Kill Bill films and some forgettable recent romantic comedies, has already been half of two power couples through her marriages to actors Gary Oldman and Ethan Hawke, with whom she has two children. And for 10 years, Busson, 45, lived with the supermodel Elle Macpherson.

In many ways, he is a more intriguing figure than his fiancée. For years he was known as “Elle’s banker boyfriend” and has only recently come to public prominence through his children’s charity Ark. Its fundraising dinners, featuring entertainment by artists such as Stevie Wonder and Prince and guests such as Clinton, Madonna and Blair, raise upwards of £25m a year.

He founded EIM, a hedge fund based in Mayfair, in 1992.

With 170 employees, it invests £6.5 billion of its clients’ funds and has contributed to a personal fortune estimated at £250m. Certainly no expense was spared on Thurman’s whopping engagement ring: an eight-carat gobstopper surrounded by 20 smaller diamonds.

Busson was born into wealth. His mother was English and a former debutante; his father a French financier. Educated in Switzerland, he has always been at home with the jet set and it was no surprise when in 1994 – after a fling with Farrah Fawcett, the former Charlie’s Angel – he met and fell in love with Macpherson. They settled in Notting Hill, west London, and had two children.

In 2005, however, the couple split. Two years later, Busson met Thurman at a private dinner in Milan. Almost immediately they became an item– and a social sensation.

Despite his financial background, Busson knows his way around the PR game. “He does all his own publicity,” said an acquaintance. “You can’t run a successful hedge fund without being very controlling. So he’s very careful about what he does and how it might be interpreted. He pays serious attention to detail – two years ago he rejected the menu for the Ark dinner four times before they got it right.”

Observers say that despite the hullabaloo surrounding them, the couple appear unaffected. “I think they’re quite normal,” said the writer Rachel Johnson. “I see them around west London wearing flip-flops: it’s like [the film] Notting Hill. I often find myself calling them Arki Grant and Uma Roberts.”

For Thurman and Busson the party goes on. Since early June, their schedule has been packed – the Ark fundraiser, Nelson Mandela’s 90th birthday dinner, Elton John’s White Tie and Tiara Ball.

Thank goodness that last Thursday they managed to get some one-on-one time over lunch. Of course they ate not at the kitchen table but at the swanky London restaurant Le Caprice. The perfect place for a superpower couple to be low key.

Additional reporting: Chloe Rhodes

Times recommends

• The real Paul Raymond
• Living in the moment
• Rent out your home and move abroad