If you’re going to fantasise about one special dress in the coming season, let it be a Balmain. This autumn, the revived French fashion house, under the tutelage of its creative director, Christophe Decarnin, is officially the hottest label out there. It’s a favourite of A-list celebrity gals — Gwyneth wore it with 7-inch heels at her recent world tour of photo calls, and Kate Hudson is a die-hard fan. Now the world’s junior jet set are queuing up to get their pretty manicured hands on one too.

Among the reasons for wanting a Balmain so much — other than its invigorating £5,000 price tag which, let’s face it, does sort the wheat from the chaff — is that it’s so hard to find one. Cash won’t help you. In order to avoid the social embarrassment of finding yourself without this season’s big number, you need to be on Facebook terms with a personal shopper at one of only three UK stockists. They will have tipped you off on the buzz about the brand last February, when the frocks were still warm from the catwalk.

“Our customers adore Balmain, but we’re having a hard time keeping it in stock,” sighs Marigay McKee, the fashion and beauty director at Harrods. “Most pieces have waiting lists, so we’re sold out before they even hit the floor.”

In the interests of research, however, McKee agrees to lend me a dress for a day, so that we might all find out what being Balmain Woman is like. And let me tell you, I feel the responsibility keenly. With only a few of these honeys in the country — and a waiting list longer than Sarah Palin’s skirts — the pressure is on.

The dress arrives in its liveried shopping bag, and I finger it with caution. Its shape brings to mind early Alaïa, with the braggadocio of Gianni-era Versace. It seems to be made of a thousand miles of stretch silk chiffon. It reeks of rich. “We’re going to have some fun tonight,” I tell the dress.

But how to wear it? Also, how not to get toothpaste on it? “Put a biker jacket over it, as Elle Macpherson would, and dress it down for a nice restaurant dinner,” suggests Helen David, international fashion buyer at Harrods. This piece of advice is key to Balmain Woman, who may be rolling in it, but is rock’n’roll, too (for what is money without fun?). It is a treat to wear a dress so thermometer-popping you need to rough it up with biker boots to make it digestible.

Tonight, darlings, the bus is hors de la question, so I take a cab. It is late summer and the Arabs are in town. Lots of them. All the way down Sloane Street and in the doorways of Harrods are groups of Middle Eastern women carrying giant Christian Dior bags on their arms with glittery Jimmy Choos peeping out from underneath their burqas. Could they be in Balmain under there?

Outside Zuma, a glitzy Japanese place that the Knightsbridge locals treat as their corner bistro, are parked five giant SUVs. Inside, it’s packed. At £8 for a bowl of edamame, it should be good, yet there is something slightly brash about this place, and I question whether BW would really spend her time here. Plus, there are a lot of women wearing white jeans with the words “Dolce & Gabbana” picked out in Swarovski crystal.

Instead, I head for the main bar at the Connaught hotel, where Anna Wintour stays when she comes to town. Madonna’s friend David Collins has recently installed a fresh look at the Connaught; he is the go-to man when you want to balance your trad with your modern. Chic enough to be a must-visit, discreet enough not to bother being a private members club, fashion friends are describing it as “the new Wolseley”.

A man in tiger-print loafers peers at me over horn-rimmed glasses. This is clearly more BW’s patch. Plans change when friends turn up. (Balmain Woman is very spontaneous. Scooting straight from a yacht in St Trop to a plane bound for Martha’s Vineyard is all in a day’s play for her.) One, a true bachelor of the global jet set, says, “All back to mine?” “Mine” is a penthouse with space to spare and a box-fresh kitchen only a housekeeper would keep that clean. Our transport is his Jag. The dress loves the Jag. It’s a natural in bucket seats at 0-60 in four seconds. It’s a fast dress.

A blink and we’re there. Coats are flung down. Veuve Clicquot is opened. A girl starts dancing and someone invites me to Ibiza next summer. A few drinks and, oh no!, is that the time? I make my excuses. Everyone looks shocked — where are my priorities? For BW’s party friends, every night’s a Saturday night (not a Wednesday, with work at 9am the next day). Alas, my carriage is about to turn into a pumpkin. As Ms David at Harrods put it, “The one thing Balmain doesn’t do is working clothes.”

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