Because last week, Topshop stores around the country were beleaguered by hundreds of crazed women who queued for hours to get their hands on the new Kate Moss collection at Topshop . . .

despite the fact that its creator doesn't even claim to have designed a stitch of the 90-piece collection.

Kate Moss for Topshop is the ultimate glorification of the contemporary celebrity-branding culture and confirms the 43year-old brand's place as the star performer in Philip Green's British retail group, Arcadia, which also includes Wallis, Dorothy Perkins and Miss Selfridge.

Last Tuesday, 300 die-hard fashion fans queued outside Ireland's flagship store on St Stephen's Green from as early as 5am in the hope of buying some of the 50 designs, which include clothes, bags, shoes and belts from 25 to 250. With military-like precision, only 15 women were allowed in at a time, and each person could only purchase five items . . . Topshop management's greatest fear was that the majority of the collection would end up on eBay.

Why would Kate Moss design for a highstreet chain?

Winning Moss's hand in collaboration is Green's greatest PR victory to date. It began with a kiss. No, really: last year the 55-year-old retail mogul paid approximately 90,000 at a charity auction to lock lips with the supermodel. A collaboration was confirmed in September, for which Moss has reportedly been paid 4.5m . . . so far.

Credited with launching trends for skinny jeans, tiny denim shorts and men's waistcoats, Moss enlisted the help of Alexander McQueen's stylist Katy England. Moss wannabes shopped so enthusiastically that Topshop in Dublin said most key pieces in the range sold out within two hours. It launches next week in Barneys New York, one of the most upscale fashion stores in the US.

How did Topshop go from teen store to fashion phenomenon?

Since its arrival in Dublin in 1997, Topshop has gone from strength to strength, appealing to both teenagers and young women.

In the last few years however, and with the opening of its flagship store on St Stephen's Green, it has gained near-cult status amongst women aged between 15 and 35.

Its main strength is its ability to copy trends from the catwalk and have them on the rails within a week of the show at an incomparably cheaper price. While it has been criticised by many for this, Topshop defends its methods by pointing out that it has given great scope to young designers by showcasing young Irish talent such as Joanne Hynes and Antonia Campbell Hughes in its stores.

The store also sustains interest by keeping key garments to relatively short runs of around 5,000, without replenishing them, to encourage shoppers to visit the store on a weekly basis.

Either way, much credit has to go to Jane Shepherdson, Topshop's former brand director in London, whose fashion instincts helped shake off the store's tacky reputation. Shepherdson and her team made Topshop not only credible but often cooler than the designers it emulated.

Shepherdson worked her way up through the ranks at Topshop, once famously taking a punt by placing a vast order for then-unfashionable tank tops . . .

and selling half a million in a week. Shepherdson not only monitored catwalk trends but also street style . . . the 'boho' style of 2004/2005, which was not seen first on the ready-to-wear catwalks, was a massive success for Topshop thanks to her grassroots approach.

When Green appointed Moss as guest designer without consulting Shepherdson, the Bristol-born executive decided to walk away.

What about the role of Sir Philip Green?

The billionaire retailer is said to take an excessively close interest in the goods on his shop floors (of which Topshop has a staggering one million square feet).

Green began his retail career at 15 when he left school to work for a shoe importer.

He made his first million by buying, turning around and then selling a failing jeans retailer, and during the '80s and '90s his entrepreneurial schemes mushroomed until in 1999 he tried to buy Marks & Spencer. That bid failed but in 2002 his dominance of the British high street was sealed when he paid the equivalent of 1.25bn to assume control of the Arcadia Group.

Will the Topshop revolution fizzle out?

With annual sales in the UK and Ireland now standing at around 900m, the only way Topshop can further expand is by growing its business overseas . . . and plans have been made to break into Russia, the US and France.

But will the rest of the world 'get' the peculiarly Irish and British obsession with cut-price seasonal trends? The 'high street' per se has no equivalent in these markets. American press have already begun to snipe that the Kate Moss collaboration lacks both originality and quality. It also seems unlikely that the label-hungry Russian market or Frenchwomen, who favour classical chic to leggings and bejewelled flip-flops, will embrace Topshop quite so wholeheartedly.

Another front Topshop will have to defend is the store's efforts to prevent labour exploitation, an issue now of unprecedented importance to consumers.

And while Moss's glamorous arrival distracted from Shepherdson's exit from the brand in autumn, once the supermodel tires of her design duties Shepherdson's finely honed talent for trend-spotting will be sorely missed.