Asos, the online fashion retailer, sustained its stratospheric growth rate over the key Christmas period as internet sales and young fashion continued to buck the trend.

Sales rose 118 per cent over the nine weeks to last Friday, outstripping the rate of growth during the rest of the year. In the 42 weeks to January 16, sales were up by 108 per cent. However, shares fell 29p, nearly 11 per cent, to 250p yesterday after Asos failed to upgrade profit forecasts. Nick Robertson, the chief executive, said that, although the rate of growth was slowing in online sales in general, he remained optimistic.

“Online is just another sales channel and, let's face it, retail is not going to have a good time of it,” he said. “But clothing online is still outperforming and young fashion is even outperforming that. We're planning for more caution than we have, but that's just prudent. We're still planning for growth.”

IMRG, the trade body of online retailers, said this month that Christmas spending online had increased by 14.2 per cent against last year, well below the 50 per cent rise between Christmas 2006 and Christmas 2007. Clothing was up by 32 per cent.

Asos attracted 5.2 million unique visitors in December and said that it had 1.2 million active visitors, a 112 per cent increase over last year. It has expanded into Denmark, Sweden and the Republic of Ireland. It said that it was on course to meet the board's expectations for full-year profit. In the past year the AIM-listed retailer increased the number of lines it offers from 6,500 to 18,000. Mr Robertson said that Asos would stock 30,000 lines by next year.

G-Star, Reef and White Stuff are among the brands to be introduced in the coming months. The downturn has pushed an increasing number of brands into considering Asos as a stockist, according to Mr Robertson.

Analysts said that Asos's sales figures were inflated by three free-delivery weekends in the run-up to Christmas, which will have eroded margins. Mr Robertson is confident that Asos's market-leading position will not be challenged soon. He said: “Our economics are different to the economics of the high street. If you have a successful store, somebody can open a shop next door. Nobody walks past you on the internet. It's hard to shake up as long as you're doing things right.”

David Stoddart, of Altium Securities, said: “Few companies, let alone retailers, are generating 100per cent-plus sales growth in the current environment. We expect online retailing to continue outperforming the wider retail market for several years.”

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