As the capital gears up for London Fashion Week this weekend, the bosses of the nation's biggest clothing chains are more likely to be found drowning their sorrows than cracking open the champagne.

But online sellers should be easy to spot on the party circuit: they will be the ones smiling.

For while the High Street is falling out of fashion with consumers, online shopping is in vogue, and the migration to the net is expected to accelerate as the economy deteriorates.

In recent months, bad news has poured out of the clothing sector. A string of profits warnings from some of retail's biggest names, alongside high-profile credit-crunch casualties such as shoe chain Dolcis, has revealed the extent to which discretionary spending is under pressure.

This week saw Next chief executive Simon Wolfson deliver a miserable verdict on the sector: there is little hope of recovery until 2010. So the last thing retailers need is to have market share snatched away by internet upstarts.

Just eight years ago, with the ignominious collapse of early fashion site Boo.com, online stores were already looking passé. But the dark days of the dot-com crash are long past.

Clothes spending in cyberspace is expected to reach £3billion this year in the UK, 6% of the total market, and Mintel forecasts this will more than double in the next five years.

The contrasting fortunes of the High Street and online stores are clear to see. Clothing and shoes sales in stores plunged at a record rate in June despite widespread discounting, but it was a boom month for the internet, with clothes sales rising 32% and footwear up 38%.

Convenience, access to a bigger product range, the spread of broadband and increased trust in the internet as a sales medium are all major drivers of growth.

A study by Capgemini and the Interactive Media in Retail Group concluded 2007 was the first year that soaring online sales really started to affect traditional bricks-and-mortar retailers.

But worse is to come for those yet to enter cyberspace: as the consumer spending squeeze continues, the bricks-to-clicks transition will accelerate as the soaring cost of a trip to town forces shoppers to opt for the mouse over the mall.

"We are bullish about the scope for fashion sales online," says Kaupthing retail analyst Matthew McEachran. "The high cost of petrol and economic downturn will drive more and more customers away from the High Street and on to the internet."

With disposable incomes plunging, Capgemini and IMRG expect consumers to develop smarter shopping habits, another driver of online sales growth, boosted by the perception that goods are cheaper on the internet.

Many retailers have long been aware of the need for a strong internet site, and have invested heavily in their online offering. These hybrid clicks-and-mortar businesses — Next and M&S being prime examples — are reporting growth online even as store sales slide.

"We are not seeing any sign of the consumer slowdown affecting online sales," says Next's Wolfson. "Over 60% of the Directory's sales are online, and there sales are up 2.2%."

But others still linger on the sidelines. Selfridges, Primark, Zara, H&M and Matalan are yet to embrace the internet with the launch of fully transactional sites.

So who are the big pure-play online winners? At the cheaper end of the sector is ASOS, adored by teen and twenty-something fashion queens.

According to Verdict Research's senior retail analyst Malcolm Pinkerton, the company is stealing market share from Next, Topshop and even Primark.

ASOS consistently wows the City with bumper figures — sales have been up 90% this year — and it is tipped to overtake Next as the number one fashion website in the UK next year.

Brokers are widely calling ASOS stock as a buy: shares in the company are as much a must-have as the latest Roland Mouret dress.

Meanwhile, Net-A-Porter is the poster-child for online luxury retailing, delivering staggering sales and profits growth.

The well-heeled increasingly turn to the boutique for their fashion fix, showing internet shoppers now trust the medium enough to fork out £6000 on an Oscar de la Renta gown. It is growing so fast that last year's sales outstripped the total for the first six years of its existence.

Analysts believe in time it could prove a considerable threat to department stores. And then there are online auctioneers such as eBay, benefiting as cash-strapped consumers search out bargains.

But surely, the spread of broadband technology — a major driver of growth — will slow, hitting the expansion of online clothing sales?

Adam Smith, chief executive of ethical online store Adili, believes this is a long way off: "Market penetration of broadband will tail off, but the consumer is still lagging in terms of acceptance of buying clothes online, so there is a big pool of potential customers who haven't yet dipped their toe in the water."

Online shopping is a trend that won't be going out of fashion next season, but should prove as timeless as the little black dress.

With the retail landscape changing rapidly and fears of a looming recession, strong internet offerings could be a major factor in High Street stores' chances of survival.