For seasoned celebrity watchers, it represented something of a watershed for Britain's social elite. Only a few years ago, the worlds of showbusiness and polo were miles apart. The only people who took any notice of what happened on a summer Sunday at the Guards' Polo Club in Windsor were either there themselves or, just possibly, the most avid readers of Nigel Dempster's gossip column.
But there has been a quiet revolution in the tweedy world of polo. It has mutated from a little-known pursuit of the landed classes to become one of the most prestigious sports in the summer calendar, and a central feature of "the season". Rather than dancing all night in Chinawhite, the biggest names of the Noughties don their green wellies and head for a muddy field. For a sport that used to be the preserve - on and off the pitch - of army officers and the county set, this is quite a shift. But how has it happened?
It is certainly not down to the game itself. This consists of eight millionaires on ponies (four per side) galloping around a field several times the size of a football pitch, with a series of rules that most spectators do not understand. The aim of the game is to hit a ball through one of the goals at either end of the pitch. In spite of - or perhaps because of - this, the most exciting fun and games take place off the field. And not all the sport's spectators are happy about it.
"Oh, the dreaded commercialisation," wails the sport's most famous advocate, the novelist Jilly Cooper, whose phenomenally successful novel, Polo, sold millions. "Of course it means the crowd will change. But then the old and bold will always grumble. Secretly I think they rather like the place to be full of film stars: it makes them feel superior."
Cooper is quite right. The woman I was seated next to - who shall remain nameless not to spare her blushes, but because she speaks for so many others - at the Veuve Clicquot Gold Cup, a main fixture in the English polo calendar, whispered to me: "Everyone here is a television presenter or an 'EastEnder'." And although that was not quite a fair analysis, it certainly was not the line-up of army officers and playboys that you might expect. There were pop stars and soap stars and minor actors and clothes designers. Polo has become a day in the country for a crowd who would feel more at home at London Fashion Week.
Many of the new fans do not understand much about polo. "I am having a great time but actually I don't know anything about it," admitted the American model Caprice at Cartier last weekend. "I really came here to look for some fit guys." And what a selection there was. Aside from the renegade royal Freddie Windsor, she had a fair choice of newsreaders (Michael Buerk, Peter Sissons and some bloke from Sky), the film star Orlando Bloom, and the singer James Blunt. These people have been invited by the sponsors specifically to get the day talked - and written - about beyond the polo yards of the Shires.
The champagne manufacturers Veuve Clicquot have been the title sponsors of England's biggest national event, held at Cowdray Park in West Sussex, for the past 10 years. In that time, they have seen the number of punters passing through the gates rise from 5,000 to 20,000.
"The famous people we invite raise the profile of the game," explains VC's brand director, John West. "Choosing polo meant that we could get instant brand recognition that would elude us if we went for something more mainstream. Nobody remembers who sponsors a football match. And it allows us to give our name to an event that attracts a crowd that is interested in champagne." Never mind the polo.
So, for the price of a lunch party in a well-appointed marquee, the brand gets mentioned in the national press and, this year, the Gold Cup final was filmed by Sky Sports. It is pretty good publicity and it comes at a price that, in advertising terms, is very competitive. VC is rumoured to pay about £180,000 for the privilege.
Cartier, the polo world's biggest sponsor, spends something like four times that on its international match day the following weekend. Audi and Rolls-Royce are also in on the act, sponsoring teams. And a host of other luxury goods brands attach their names in different ways.
Away from the corporate hospitality that accompanies big matches, traditional polo types still run the game. But even Simon Tomlinson, the patriarch of an old polo-playing clan, who now owns the Beaufort Polo Club (and whose son, Luke, one of the world's best players, was arrested for invading the House of Commons), tells me he has just employed a professional PR man.
"Polo has always had, and always will have, a reputation for involving people who are rich and it has that cachet about it," he says. "So what we sell to sponsors is, for example, that their guests may have the chance to speak to the Prince of Wales. At the same time, a lot of people who come for that reason discover the joys of the game. You need to be well coordinated, a good team player, and an excellent horseman, but other than that, anyone can do it."
Anyone - you understand - is a relative term. It has only recently become possible to play without owning your own ponies, even as an amateur. At the highest level, a pony can set you back £50,000 and, to play, you need more than one. In the course of a top-level match, each player can get through eight ponies. The professional players can earn six figures during the English polo season before being flown - ponies and all - to America.
The best players are snapped up to join teams owned by some of the richest men in the world. So far, so normal: that, after all, is how sport works. But in polo, there is a twist, because the team owners (or patrons) also get to play. They have not just the thrill of a dangerous sport, but also the excitement of knowing that their cash has bought them a place at the front of a team consisting of truly excellent players. "It would be like that Russian man [Roman Abramovich] playing in goal in football," Jilly Cooper explains.
It has always worked like this. Big business men buy into it; Arab sheikhs burn oil money on it; even retired rockers like Mike Rutherford of Genesis and Kenny Jones of The Who spend their hard-won "golden disc" earnings on it when they retire to the country. But, at grassroots level, polo is undergoing something of a revolution. It is now played across the country at Pony Clubs, in schools and at universities. Simon Tomlinson prefers to ascribe the game's present success to this, rather than to the corporate sponsors and celebrity attendees. David Edelsten, the polo correspondent for Country Life and The Field, explains that it is all about having fun.
"Celebrities are welcome to their days out," he says. "But you really only see the tip of the iceberg at the Cartier International. The sport is really growing because it is becoming more popular at a lower level. You can pick up a couple of ponies second or third hand, and once you've hit the ball, you never want to stop."
The displays of horsemanship on the field are impressive. The coordination and skill required are immense, even if the speed of the action means it isn't one of the world's greatest spectator sports. But it has its fans. Ponies - and pitches - are borrowed from local enthusiasts, and people who have never been on a horse before are starting to play.
For those of us without the coordination, or inclination, or budget to jump into the saddle, there are opportunities for spectators to join in too. At half time, there is the traditional "treading in the divots" when the crowd wanders about the field, ostensibly to make the ground even. As often as not, the high-heeled shoes damage as much as they repair, but it is a good opportunity to spot friends and invite them to your picnic spot for tea. There is nothing like proving your hamper superior to your neighbour's.
Just as these traditions continue alongside the innovation, so the big events still attract country grandees to sit with television celebrities. The Prince of Wales is still the world's most famous player. This year, Prince Harry attracted some publicity for his miraculous recovery from a "bug" that was keeping him off duty at Sandhurst but cleared up in time to play an exhibition match at the Cartier International. Back in 1988, Diana, Princess of Wales, was photographed presenting her lover, James Hewitt, with a polo cup. And people with an even longer memory remember her meeting Prince Charles at a match in 1970.
The old timers may bemoan the fact that Sienna Miller and her ilk now stand alongside the Princes as the public face of their sport. But the fact that every sort of modern celebrity can shake hands - and pose for the cameras - at a polo match means that the game's future is assured.
"All the polo regulars were having a giggle at a woman who looked like a lampshade," says Jilly Cooper of a recent match, disapproving as much of the people laughing as of the lampshade herself. But then who is Cooper to talk? After all, Polo is on the verge of being made into a film starring - you guessed it - Sienna Miller.
The rules of the game
In its modern form, polo was devised by British cavalry officers, who saw it played in India. Its prehistory, however, is as old as the civilised world. It was played from Constantinople to Japan throughout the Middle Ages and men on horses wielding sticks can be found on ancient pottery.
The playing field is 300 yards long and there are four players, all on horses (always referred to as ponies) on each team. The game is split into sections called chukkas. There are six chukkas in a match, each lasting seven minutes. Between each chukka, there is a three-minute interval, and another break of five minutes at half time.
Polo teams combine professional and amateur players. The owner of a team - the patron (pronounced the French way) - usually plays at the front of the field, with the professionals behind him.
Players are ranked annually and given a handicap. The best players in the world have a handicap of 10; many of the patrons will have a handicap of nought. The worst fall into minus figures.
Who's who on the polo field
The 30-year-old England polo team captain.
Outspoken editor of the Polo Times. Well-known for campaigning against influx of foreigners into English teams, and being Henry's mother.
The Tomlinson family
Luke invaded the House of Commons with Otis Ferry, while brother Mark is tipped as a future England captain.
Captain of Gold Cup winners Dubai.
The UK's 70th richest man hosts polo's most prestigious competition, the annual Gold Cup at his 17,000-acre estate in West Sussex.
Veteran Mexican player, holds record for the most Gold Cup victories.
Commentator - he is to polo what John Motson is to football.
The Kidd family
Polo-playing supermodel Jodie and brother Jack run an events company specialising in match hospitality.
The Royal Family
Charles and William have helped raise the profile of the game, but real praise must go to Harry, whose team won the Cartier International competition last week.
Chief executive of Hurlingham Polo Association, the governing body.
Additional reporting by Jonathan BrayReuse content