"Because we are Italian, we are really spontaneous," explains Stefano Gabbana, one half of design duo Dolce & Gabbana. "And sometimes, when pop stars ask to borrow clothes, I say no - I say no because I don't have the time or maybe because I don't like the people, I don't like the singer, I don't like the song. I asked George Michael many times if we could dress him, and he said no. Not in a bad way. He said, 'No thank you, because I have everything already, I really appreciate it but I don't need it.' And on his last album, Patience, he was wearing our sunglasses, and I say, 'Thank you so much!'"

Strange as it may seem today, there was a time when the idea of blending pop music with designer fashion was novel. Of course, there was always a handful of musical visionaries who saw the value of a distinctive sartorial image: Elvis, Debbie Harry, Michael Jackson and David Bowie, to name but a few. But those stars were more likely to approach a specialist costumier than a fashion designer, to create their on-stage personae.

While the fashion circuit and the rock fraternity often overlapped - for example in the case of Bianca Jagger, muse to Yves Saint Laurent - it wasn't until the 1990s, and the dawn of the self-conscious "celebrity brand", that ready-to-wear designers made explicit partnerships with music stars.

Among the first fashion designers to make a powerful alliance were Dolce & Gabbana, who at the beginning of that decade were still considered to be newcomers with much to prove.

While Gianni Versace embraced and, to a certain extent, created the supermodel generation, and Giorgio Armani laid claim to the Hollywood establishment, it was Domenico Dolce and Stefano Gabbana who courted the attentions of pop stars most assiduously.

Madonna, Kylie, Beyonce and Whitney have all sparkled in the designers' multicoloured crystals, or been cross-laced into signature corsetry-inspired dresses; Justin Timberlake, Sting, Ice Cube and Lenny Kravitz have allbeen made over as pinstriped gangsters or musclemen.

"I love Kylie, I love Lenny Kravitz,I love Sting, I love them all," coos Gabbana. "Every one of them is an icon. I love Pavarotti. We've dressed Pavarotti, many times."

To celebrate their ongoing relationship with pop artists, a glossy new book, entitled Music, is being published in the UK this month, with a portion of proceeds going to an Aids charity.

As if to prove the designers' clout among rock royalty, three generations of Presley women - Priscilla, Lisa Marie and Riley Keough, a model and the image of her grandfather Elvis - arrived en masse for the book's recent launch in Italy, a feat which only US Vogue, for a cover shot, had previously pulled off.

This was all part of what is now a remarkably successful strategy for Dolce & Gabbana, which sees the famous logo and brand promoted far beyond the fashion magazines and into the sphere of MTV and VH-1, album covers and world tours.

"In the beginning, when nobody knows you but everybody knows the pop star, ordinary people say, 'Why do they wear these clothes, who is the designer?'" says Gabbana, the tall and tanned native Milanese, and the more talkative of the pair. "And then, you become famous, little by little. It's a good ad for us. You don't make money but you become, you know, popular."

Most impressively, Dolce & Gabbana were among the first designers to dress Madonna, perhaps the most famous mannequin in the world (her celebrity has also added lustre to Jean-Paul Gaultier's career, and to the house of Versace).

The Material Girl hired them to create 1,500 costumes for her Girlie Show tour of 1993; they also designed her famous rhinestone cowgirl look for her Music album four years ago.

"That was an inspiration between Elvis and cowboys," says Gabbana.

The pair first realised that they had caught the singer's attention in 1991 when, in a scene from her movie In Bed With Madonna, former lover Warren Beatty rushes backstage after a performance to present her with an enormous black box, printed with the D&G logo. The designers admit that - during the fitting process - Madonna was the only performer who ever made them feel star-struck.

"She was the one singer who made me feel nervous - me and Domenico, both of us. We love her, and we knew her from the beginning. I'd seen all her different faces, as a singer, movie star, mother, lover. She was the first pop star to ask us for something, and we loved her from a long time ago. People like that, they can make me anxious sometimes."

Since the Girlie Show tour, which featured heavily crystal-encrusted bustiers, the designers have also provided exclusive costumes for many tours, including Whitney Houston's in 1999 and Kylie's in 2002.

Perhaps predictably, Gabbana is keen to paint the brand's relationship with musicians as a meeting of creative minds rather than mere product placement.

"It's like a collaboration," he says, through a heavy Italian accent. "I inspire the pop star and the pop star inspires me. We learn from music a lot - for example, from the tour of Kylie Minogue, from Madonna, from Bono - we learn a lot, you know?"

Judging by the dozens of image transformations documented in the book, it seems that plenty of formerly ordinary-looking singers have gained a lot from these designers, who have helped to turn them into larger-than-life stars.

Expert at cantilevering the female form into corseted dresses, adding glitz with lavishly beaded jeans, or delivering a slick androgynous look with satin tuxedo suits, surely Dolce & Gabbana, who set up their first studio in 1982, know exactly what they're doing.

What do they have to learn from pop singers?

"Well, a fashion show and a tour are to-tally different!" exclaims Gabbana. "The pop star needs to change in 30 seconds, so maybe we need a fake button, a lot of zips, different straps - we learned all this. We learned that they need something for the movement of the arms - that you need more fabric under the arms, or stretch fabric."

Dolce & Gabbana aren't beyond open homage to their favourite pop icons, either, having based entire collections around both Elvis Presley and Madonna - even putting the latter's face on a T-shirt (sprinkled with rhinestones, naturally).

Above all, they are, Gabbana says, simply music fans. "This book was something like an award to these people in music, because music inspires my life," he continues, dreamily.

"When I wake up in the morning, I open the CD player. I want to hear music all the time, when I work, in the car, on a Saturday night when I go dancing. Music is my life!"

* Music: Dolce & Gabbana' is published by Assouline.