In this December 21, 2000 photo, Madonna waves to the crowd as her then-fiance Guy Ritchie holds their son Rocco after his baptism at Dornoch Cathedral, Scotland

Madonna, who turned an unconvincing 50 at the weekend, is on the brink of a new tour — and inevitably it is generating a fashion frisson. For rather than opting for Country Casuals and elasticated waistbands, the woman who has enjoyed more incarnations than Proteus himself will, as ever, push the sartorial boundaries.

The Sticky & Sweet tour, which opens in Cardiff on Saturday, features an intriguing mix of gangsta pimp, dominatrix and gypsy costumes. And with looks designed by Givenchy’s Ricardo Tisci, shoes by Miu Miu, thigh-high boots custom-made by Stella McCartney and sundry items from Yves Saint Laurent and Roberto Cavalli, it leaves no fashion stone unturned.

Although eyebrows are occasionally raised at the singer’s off-duty wardrobe — her penchant for grubby tracksuits and silk bloomers, not least — her stage attire provokes nothing but awe.

In this July 20, 1990 photo, Madonna performs during her Blond Ambition tour in Wembley Stadium in London

“Madonna was the first of her kind,” says Lorraine Candy, editor of Elle magazine. “Stars such as Debbie Harry, Patti Smith and Jane Birkin had distinct looks and their own natural styles. But Madonna really entered into the fashion world. Her relationship with Gaultier made her like the supermodels of the time. It’s never a catwalk look, it’s creating a whole new self, and exploiting cultural references to get this self talked about. In doing so, she transformed herself into a brand.”

One woman has been Madonna’s collaborator on this venture since 1997 — equivalent to at least a century in fashion years. Arianne Phillips, 45, and based in LA, first met the performer at a shoot for Rolling Stone magazine, and has styled her concerts ever since.

“I had been an admirer of Madonna for years,” says Phillips, “idolising her awareness of visual style, her sensibilities, her forever moving forward. I never dreamed I’d get to work with her.” Phillips has also styled Justin Timberlake and Courteney Cox, yet her own appearance belies her guru status. “You wouldn’t see me and think: ‘There goes Madonna’s stylist’. My look is pretty low-key: lots of black, nothing that screams fashion, apart from the alert look on my face.”

Madonna performs at the beginning of the 41st Annual Grammy Awards at the Shrine Auditorium in Los Angeles, February 1999. This was her geisha look, especially cultivated during the days of the hit single Frozen

Phillips also helps Madonna with album covers, film and theatre appearances and award ceremonies, maintains a separate magazine and film career, and was nominated for an Oscar for the costumes in the Johnny Cash biopic Walk the Line.

It is touring, however, that is the most strenuous role. Not only does the diva herself require dressing, but Phillips must also take responsibility for the 26 other performers. She marshals the work of other designers and creates a good deal of the outfits herself — a role she describes as “the perfect synergy between styling and costume design”.

For this, their fourth tour, there will be four motifs. The first, a dominatrix-style gangsta pimp/Art Deco look by Givenchy; an “Old School” phase harking back to Madonna’s early days in New York; a paean to Romany romance, also courtesy of Givenchy; and a futuristic rave moment rich in Japanese influences.

Candy’s favourite outfit is the gypsy look. “It feels most now,” she says. “The colours are very strong, and there’s that religious element going on. As ever, she’s saying: ‘Look at my body.’ And why wouldn’t she? It must be Olympic standard.”

Madonna performs during the opening of The Virgin Tour in Seattle in April 1985

Other conspirators, notably Italian label Dsquared’s Dean and Dan Caten, who created 150 pieces for Madonna’s tour in 2000-01, have remarked upon her control-freakiness. “She is amazing,” says Dan. “She knows exactly what she wants.” Phillips concurs: “Madonna is 100 per cent involved.”

More even than the leather-look Rolling Stones or the still sprightly Tina Turner, Madonna’s age attracts comment. Her position is robust. “I’m not going to be defined by my age,” she says. “Why should any woman?”

Lorraine Candy agrees. “The age thing is irrelevant,” she says. “As someone who has just turned 40, I’m really bored by being told what’s right for a certain age. We should wear what we want to wear. Madonna’s body may be unique, but we can all learn something from her spirit of transformation — her attitude.”

In effect, Madonna’s chameleon quality makes her the embodiment of fashion. “No one else is able to do that reinvention, and that’s what fashion is,” says Candy. “Someone like Posh Spice looks like the puppet of designers. The clothes wear her. Madonna wears the clothes.”

Which is your favourite Madonna look?

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