The Big Question: Are celebrity-designed clothes any good, or is it just branding?

Why are we asking this now?

The flamboyant Italian designer Roberto Cavalli's collection for high street shop H&M went on sale yesterday. It features 20 men's pieces and 25 women's pieces, including underwear and accessories, and the defining motif of the women's range is animal print.

Is this justanother celebrity endorsement?

No. Cavalli does have strong celebrity associations, having dressed the likes of Beyoncé Knowles, Jennifer Lopez and Victoria Beckham (don't let that put you off), but he is primarily a successful, high-end designer who shows his collections in Milan.

But is the high street in the grip of big-name collaborations?

The high street and its shoppers have been in thrall to big names ever since Karl Lagerfeld designed a range for H&M in 2004. But it wasn't the first of its kind. Jasper Conran collaborated with Debenhams in 1996, and many other designers followed suit. Coco Chanel and Christian Dior both sold their designs to the mass market. But now it's not just designers who lend their names and expertise to clothing ranges – celebrities with no formal training have got in on the act. Madonna has worked with H&M, Kate Moss with Topshop, Penelope Cruz with Mango, and Lily Allen and Kelly Brook have collaborated with New Look.

Do the celebrities actually design the ranges themselves?

They don't design in the pure sense. They have what is known as "input" – working with a team and giving opinions. Topshop has said: "Kate Moss has had a huge input in the range at every level, from the design concepts to the fitting and the logo. Top designers like John Galliano don't cut patterns, they have pattern cutters." Moss has never claimed to have created clothes from scratch, saying she "didn't want to be a 'designer' designer and have to do shows and all of it."

What do real designers think of what's happening?

Designer Jeff Banks might not be the most high-profile name in the fashion industry but he expressed what many other designers feel when he said: "Can Kate sharpen a pencil or draw a matchstick man? I wouldn't put money on it. I'll bet she just grabbed one of her many Prada bags, rifled through her wardrobe and turned up at Topshop's head office in Oxford Street for a quick hour's briefing with the in-house designers and buying staff." It is the up-and-coming, or less well-known designers, who resent celebrity names the most because they focus attention on glamour and name recognition, rather than innovation and quality.

Having said that, Topshop features ranges by new or cult designers such as Marcus Lupfer and Marios Schwab. These provide the designers with a financial boost and introduce experimental creations to a mainstream audience. Gap has helped to boost the profile of cult, but not widely known, designer Roland Mouret and most recently, the shoemaker Pierre Hardy.

Do celebrity ranges always give retailersa boost?

It's not easy to ascertain exactly how well a range has done, as companies don't tend to break down figures in such detail. Their value may lie in adding to the overall profile of a brand, rather than notching up specific sales. At Arcadia, which owns Topshop, profits are up this year from £288.6m to £293.3m after a 2.1 per cent rise in like-for-like sales. Owner Sir Philip Green said of the Kate Moss collection: "It has been very successful and it's now selling in 21 countries." But then he would say that.

While many first runs of celebrity collections have caused queues round the block and media hype before selling out, the clothes are often left on the rails after the initial excitement subsides. Many Roland Mouret dresses went into the Gap sale, as did Madonna's range for H&M.

Which ranges have been hits?

Ranges by professional designers are much better than those by celebrities or models. H&M's designer collaborations – with Karl Lagerfeld, Stella McCartney and Viktor and Rolf have been fairly strong. The range by Viktor and Rolf featured trench coats, dresses and shirts with signature heart motifs that looked far more expensive than they really were. The statement dresses in the Cavalli range – with beaded, leopard print and metallic finishes – will appeal to fans of the designer's sexy, extrovert aesthetic. But there are also pieces, such as a rock chick serpent bracelet, that are more trashy than glamorous.

So are the celebrity ranges up to scratch?

Madonna's range for H&M was abysmal and totally lacking in any creative imagination or flair. Droopy dresses, synthetic tracksuits and waitress-style shirts deserved to be left unsold at a jumble sale. Moss's ranges for Topshop have included a few nice pieces – especially among the dresses – but attracted criticism for being copied from vintage outfits in her own wardrobe. Items such as hotpants and skin-tight maxi dresses are also deeply unflattering to anyone over a size eight. Surprisingly, Kelly Brook's swimwear and lingerie ranges for New Look have been quite good.

Overall, is this good for the customer?

Yes and no. When a designer range is as good as Viktor and Rolf's for H&M, it means people who are interested in cutting-edge, high-end fashion can buy visionary designs at affordable prices. It also arouses interest in the fashion industry and design generally – raising awareness of clothing as an art form and not just an endless stream of trends with no cultural context.

The downside to big-name ranges is that people can flock to buy them because of the brand, rather than responding to and developing their own taste. Worse still, they might buy them to sell on auction websites such as eBay, turning what should be partly a process of design appreciation into a cynical, wholly commercial transaction.

Similarly, anyone who has ever queued for a celebrity range will know that they can encourage an aggressive and acquisitive side of human nature. Customers fight, snatch and elbow each other to own a piece of clothing supposedly touched by the hand of 21st-century fashion's new god – celebrity.

Should shoppers take any notice of clothes designed by celebrities?

Yes...

* When designers collaborate with the high street it democratises high fashion

* It shows that good design does not have to be prohibitively expensive

* It creates excitement and interest in the fashion industry

No...

* Why should celebrities with no professional design training be favoured over 'real' designers?

* It creates acquisitive, celebrity-induced hysteria rather than design appreciation

* Quality and innovation suffer in favour of name recognition

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