Soaring sales on the web are expected to account for more than half the retail growth in Britain by 2012.

More than half of all the sales growth in Britain's retail sector over the next four years is expected to come from the internet as more consumers switch their preference from the high street to the worldwide web.

A new survey claims that the value of online retail sales is expected to soar from £20billion this year to as much as £50billion by 2012 - nearly 15 per cent of the total retail market.

Olivia Gillan, retail partner at PricewaterhouseCoopers (PwC), said: “Basically, more customers are choosing to shop around the clock.”

Much of the online growth is expected to come from Britain's most powerful retailers. The John Lewis Partnership has launched a new “click and collect” service in the latest expansion of its internet service.

This will allow customers to order products over the web for collection at either of the John Lewis department stores in Bluewater, Kent, or Milton Keynes. If the trial is successful, it will be rolled out across the company's stores around the country.

On Thursday Marks & Spencer is expected to show that, in a rare piece of good news, it is well on the way to reaching its target of generating £500million of annual sales over the internet by 2010. Sales at Asda.co.uk in August were 80 per cent higher than a year ago, while Ocado, the delivery group linked with Waitrose, recorded a 20 per cent improvement.

Ms Gillan believes that the rapid growth of the internet stems from time pressures on consumers, the fact that they are far more comfortable shopping online and the much- improved look, functionality and service offered by retailers on the web.

Asos, the fashion retailer, has virtual catwalks, where models showcase the clothing. Numerous other websites carry video. Ms Gillan said: “The internet is growing because the quality of what you can now get there is much better.”

Online growth is only likely to increase pressure on the more traditional high street.

The Times revealed two weeks ago that industry experts believe that the number of empty units on the high street is averaging about 10 to 15 per cent as customers shop online or travel to new edge-of-town shopping centres.

Ms Gillan said: “I think the growth of the internet is going to have a big impact on the high street, particularly around secondary and tertiary locations where you don't have the experience you get in a big shopping mall.”

PwC's forecasts exclude airline and travel websites, which are included in the projections used by IMRG, the web monitoring company, which last year predicted that the internet would account for half of total retail sales by 2018.

Despite all the optimism, there are clouds in cyberspace. Last week IMRG indicated that some internet retailers were beginning to feel the effects of the credit crunch, with year-on-year sales growth slowing to 15 per cent in August, against 30 per cent earlier in the summer.

Mike Petevinos, head of consulting for Cap Gemini, the IT consultancy, said that there were signs that customers were beginning to mirror their behaviour on the high street and look for value when they went online. The trend is reflected by traffic figures from Hitwise for the week to September 20. Aldi, the discount supermarket chain, was the third-most visited grocery website, despite the fact that it does not offer a home shopping service.

Mr Petevinos said that the internet was likely to be a dominant factor in the run-up to Christmas.

“It is important to acknowledge the inevitable impact of faltering consumer confidence, with shoppers opting for lower-cost accessories in preference to big-ticket items,” he said. “But online will continue to outperform the high street and we still think that in October, November and December online retail sales will be around 60 per cent up on last year.”

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