Online purchases now account for 10 percent of all retail sales, according to new research by the Interactive Media in Retail Group (IMRG), and the proportion is still growing.

The IMRG Index report, published this week, says consumers are spending £50bn each year online, and a further £30bn of offline retail sales are influenced by customers' activities on the web, such as product research.

The report shows that retailers which co-ordinate their offline and online operations will attract and retain more customers, said IMRG chief executive James Roper.

In the six years since the IMRG Index started, online retail sales have grown 2,000 percent and they are set to grow further. Fifty-two percent of respondents said they intend to reduce high street spending, and 45 percent intend to increase online spending.

"Traditional organisations often have the impression that the web site is only a small percentage of what they're doing," said Conrad Bennett of web analytics specialist WebTrends. "So these figures are a great justification for the interactive teams for the efforts they're making [on the online side]."

Bennett said firms must continue to research and evaluate their position in their markets and the behaviour of visitors to their web sites, to ensure that potential customers are not researching products and services online but then buying elsewhere.

Amazon, Dell and Argos took the top three spots as most popular retailers in the IMRG's Hitwise top 50 list. Firms with an online-only presence dominated the top 10, and the travel industry also featured heavily in the list. Online booking firms and airlines accounted for nearly 40 percent of online sales.

"The surprising thing about this list was the number of key brands that aren't there," said Roper. "Why are [large, well-known] firms like Boots, Ikea and Selfridges not on the list?"