Ilse, however, has no problem in conjuring up an Elle Deco-style home for her trousers. "There's the Sixties inflatable look, of course," she says, "but for more user-friendly furniture I'd look at the transparent PS chairs from Ikea. A bit of pale Danish wood and those Kartell plastic trollies... Soft latex curtains might be rather beautiful," she adds, mentally clocking the picture for a future issue, no doubt.
The present issue of Elle Deco, however, is the one we are here to discuss, because it is guest edited by Joseph - a man famous for the style and content of his eponymous fashion shops, so famous in fact that he is only the second Joseph in history not to need a surname.
Guest editing is a curious concept from America, where every so often readers are happy to believe that some terribly famous person like Madonna or Bill Clinton sat in the editor's chair of a glossy magazine with a blue pen. Over here it is greeted with more scepticism. "Find out more about this guest editing business," urged my commissioning editor, "it sounds like a good way to get a month's holiday."
Actually, it was the bizarre notion of Nelson Mandela "editing" an issue of French Vogue (which he did two years ago after the Dalai Lama) that most inspired Ilse. She, however, has banished the notion of a holiday and gone for slightly less incongruous partnerships - with people from the world of design who can put their own visual stamp on the magazine. Terence Conran was the first guest editor, of the June issue which featured his apartment, junk furniture, "factory funk" and cigars aesthetically stubbed out in ashtrays or jammed between his lips.
Working with Joseph was quite different, says Ilse. "Terence was clear and logical, while Joseph put his feelings into the whole thing. He is totally intuitive and relies more on other people. He wanted pictures that told a story, a feeling, and some that had humour. The clear graphic- look-in-a-studio was not his cup of tea at all."
Joseph himself - small, fiftyish, bristling with energy, with an impish grin and a French accent that 30 years of living in England has done little to diminish - has always been at the cutting edge of interiors when it comes to shops. Norman Foster designed his first big store in Knightsbridge 20 years ago.
Joseph recalls with embarrassment how he had no idea, when someone suggested the name, that Foster was such a big fish. "I was a bit surprised when we had to make an appointment three weeks in advance," he says. "When my brother and I turned up at his office, and saw all the photos of his work, I just thought 'Let's get out of here', because we had no money."
Just as Foster was telling him the same thing, his first wife, who shopped at Joseph, appeared and smoothed the way for one of the first high-tech fashion shops. It gave Joseph a taste for working with the best. He then worked with Eva Jiricina, the Czech architect, one of the best exponents of "beautiful bones" interiors. The store she worked on for him was perhaps the most succesful, its simplicity and strength of materials having a warmth that the more pared-down interiors of his later shops lacks.
In the matt-black period of the Eighties, Joseph branched into homeware. "I was in Dean and Deluca [the ultra-hip deli] in New York, and looking at the customers. They had this shine in their eyes; they were getting excited by a beautiful cauliflower. Back in London, people were looking at wonderful, expensive clothes with dull eyes. They didn't get excited any more."
That was when he opened Pour La Maison, his now defunct store on Sloane Street. It sold not cauliflowers, but anything stylish from dustbins to chairs - most of it black - alongside the clothes. "It was great," he says, "but after a while other shops started to do it too, and it lost its charm. That's the trouble with these waves of fashion. After a time I came to hate the Le Corbusier leather chair because there was so much black around. Black is a lovely colour, but in the Eighties it got too much: people were wearing four layers of black. Things are lovely, I think, when they are not exaggerated."
In his own home there is no exaggeration, but there is a lot of brown - various shades of mushroom and caramel. "When surrounded by so much colour at work," he says, "you need to come back to somewhere peaceful."
With his aversion to the "waves of fashion", it's easy to see why Joseph's home has become a haven of calm. Though the time-lapse between fashion and interiors is becoming shorter and shorter (grunge interiors followed hot on the heels of grunge clothes two years ago), homes will always have a more lasting foundation of style because of the expense involved.
Joseph's last home was a large flat with a living room the size of a ballroom: very glamorous, "very Joseph", everyone said. By then he and his wife Isabel had a baby, Gigi, and as he put it "the pram looked wrong there. If something you do every day in your home becomes wrong, it is no longer a home."
You get the feeling that Joseph and Isabel surprised themselves with the place they bought next - a 1930s house that could, at a pinch, be called suburban if it didn't have such an impeccable postcode. The pushchair is at home here (though tidily concealed), and so, clearly, are Joseph and Isabel. Now that the house has been thoroughly remodelled inside by Parisian decorator Christian Liaigre, they no longer feel they have to justify their house choice to style watchers.
Joseph wanted a designer who was somewhere between the architectural minimalists he had used over the years in his shops, and the flouncy interior decorators. "One is too minimalist, the other doesn't know where to stop. When you have a family and you get a little older, you want a bit of warmth."
This is not, however, a cosy clutter of domestic warmth. As we sit in a corner of the large entrance hall, Joseph remarks that it is "like the foyer of a hotel - except that a hotel is not personal, and here we have the feel of what we like." I'm glad it was Joseph, not me, who likened his home to a hotel lounge; coming from anyone else, it doesn't sound like a compliment. But he likes the neutrality of hotel rooms, finding them relaxing - presumably in contrast to the excesses of fashion:
"This is the sort of house where you can push the furniture back, and it's a great place to have kids to play in the afternoon. In the evening it all goes back into place when you have people for dinner."
The ground rules of a good interior are pretty much the same as for a good wardrobe. "It shouldn't be gimmicky," says Ilse Crawford, "but you need good basics with the odd perky thing to make it more fun."
For Joseph "good basics" means a good floor. In Elle Decoration he is photographed in a passionate embrace with his upstairs carpet. Downstairs, the floor is a good but simple wood. "The floor determines the mood of everything," he says. "It gives you a feeling of respect for the place. When I go into a great museum, everyone else is looking up at the famous paintings but I am looking downwards at the floor."
Joseph supposes his fascination with flooring in particular, and interiors in general, came from his early childhood in Morocco; he lived in a big Casablancan house with his grandmother. "There are great floors in Morocco," he says. "I remember my grandmother throwing buckets of water on to the floor to clean it before guests came for lunch, and she was always moving the furniture around. It was very Thirties inside, which is why I have, an affinity with that period style."
And "something perky"? That, undoubtedly, has to be his daughter Gigi, who has her own realm at the top of the house. While we have been talking, she has been playing with Isabel, who has generously provided creche facilities for the unannounced excess baggage - my three-year-old daughter. Gigi has the best playroom in the world, we are all agreed. It is fitted out like a small nursery school, with easels, a trampoline and professional units and storage cupboards in pale wood. A child-size opening in the wall leads to a kind of living Wendy house.
On the way home, I realise that I only noticed Isabel's dazzling smile, not what she was wearing. It must have gone with the house, and it was definitely not white plastic trousers. My daughter sits munching a bag of crisps in the back of the car and experiments with the philosophy of envy. "I'm lucky to have this packet of crisps," she says, "and Gigi is lucky to have her playroom." It's a nice thought, but sadly it doesn't work for grown-ups. I'm just jealous.
- Joseph is guest editor of the December/January issue of 'Elle Decoration'.
JOSEPH'S ADDRESS BOOK
MUJI, 26 Great Marlborough St, London W1 (0171-494 1197 for mail order). Also 63-67 Queen St, Glasgow G1 (0141-248 7455). Beautiful basics, uncontaminated by fashion.
EGG, 36 Kinnerton St, London SW1 (0171-235 9315). How a shop can be so totally unmaterialistic and sell such simply covetable clothes and objects is a mystery that can only be explained by the attitude of its owner, Maureen Docherty, one of Joseph's heroines.
DAVID GILL, 60 Fulham Rd, London SW3 (0171-589 5946). Joseph's favourite antique dealer, good on 1940s.
PORT OF CALL, 13 Walton St, London SW3 (0171-589 4836). Decorator Mimmi O'Connell's eclectic mixture of English, Irish, French and Oriental antiques and decorative items.
MARYSE BOXER AND CAROLYN QUARTERMAINE, Chez Joseph, 26 Sloane St, London SW1 (0171-245 9493). Distinctively decorative china, fabric and accessories.
DAVID MELLOR, 4 Sloane Square, London SW1 (0171-730 4259). Beautifully simple cutlery, kitchenware.
VALERIE WADE, 108 Fulham Rd, London SW3 (0171-225 1414). A treasure trove of decorative furnishings: leopard and zebra print carpets, mother-of- pearl furniture.
THE CONRAN SHOP, Michelin Ho, 81 Fulham Rd, London SW3 (0171-589 7401). "Of course," says Joseph.
PULBROOK & GOULD, 127 Sloane St, London SW1 (0171-730 0030). "A traditional florist," says Joseph, "but you know you are never going to be disappointed with what they do."
PETER JONES, Sloane Sq, London SW1 (0171-730 3434). "A wonderful institution. They do their job so well."