We used to think of luxury as caviar, champagne, private jets, diamonds and penthouse suites. But it isn’t that simple any more. Take, for example, the expectations of two luxury-aware women who were rubbing shoulders the other day: Melania Trump and Camilla. Now, Melania has a straightforward, traditional take on luxury: for her, it is a wardrobe full of Vera Wang couture, jewellery requiring its own security detail and million-dollar parties. For Camilla, it is getting into bed at Highgrove, still in her jodhpurs, with the remote control and a microwave-heated fisherman’s pie from M&S. You know that the luxury of commissioning a wardrobe for her American tour was entirely lost on her, as were the merits of that tiara, which Melania would have killed for.

If the definition of luxury is having your most indulgent desires met, and then improved upon, what you desire depends entirely on who you are. For Coleen McLoughlin, it happens to be £25,000 worth of hand-printed wallpaper; for Gwyneth Paltrow, it’s a stint at the Ashram, that exclusive, alcohol-free yoga retreat in the Californian hills. Luxury is no longer automatically about Cristal and foie gras, or even treating yourself. It can just as often be about getting back in touch with what’s important, taking time, looking after yourself.

If you’re Sarah Jessica Parker, luxury is not, I’m guessing, getting made over by your personal stylist, make-up artist and hairdresser (most women’s ultimate indulgence), before heading out to the chicest restaurant. Rather, it’s lying in a flotation tank, or walking on a private beach, alone.

If you want to find out what the really rich call luxury at the end of 2005, then the quickest route is to check out how they are holidaying. Negative luxury is the new thing — rooms stripped of frills, simple food, an informal dress code, unpretentious architecture, lots of space and privacy and absolutely no nightlife. Those who are responsible for setting the luxury agenda want sand between their toes at the bar; they want to be fed healthy food, not the richest ingredients money can buy; they want to take off their Rolexes and pretend they are lost on a smooth-functioning desert island. Nobody wants to dress up, or show off, or get drunk. They’ll pay £2,000 a night for the privilege of what Melania would consider to be slumming it.

Negative luxury has already had an impact on the lives of those of us who aren’t so accustomed to conventional luxury that we feel the need to escape it. Sushi and sashimi are negative-luxury foods — would you rather have the foie gras and the lobster? We want flaky white furniture or Oka catalogue stuff, as opposed to valuable antiques, even if the relatives are offering. We drink wine in preference to champagne, and feel better driving a Smart car than we would a Rolls-Royce. Everyone still dreams of fresh sheets, their own cook, a 24/7 chauffeur. But something is changing.

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