British consumers will spend 19.3 billion pounds ($30.5 billion) by 2021 on purchases using their mobile phones as technology advances and more people have smartphones, Barclays Corporate estimated.The figure will rise from 1.3 billion pounds now, encouraged by systems such as Near Field Communications and faster mobile data transmission, Barclays Corporate, a unit of London-based banking group Barclays Plc (BARC), said in a report. Food and groceries are the biggest category, with mobile sales of almost 300 million pounds this year, according to the report.“With little new shop space coming into play, the real growth opportunities lie on the virtual high street,” Richard Lowe, Head of Retail and Wholesale at Barclays Corporate, said in the statement. “Those retailers which are prepared to invest will be at a significant advantage to the competition.”Mobile commerce will grow by 55 percent over the next five years, according to Barclays. It said just over half of shoppers already use their mobiles at some stage of purchasing.Vodafone Group Plc (VOD) and other wireless operators said in June they had agreed to create a common platform for mobile payment systems to speed up the development of additional services in the U.K.Vodafone, Telefonica SA (TEF), and Everything Everywhere, the partnership between France Telecom SA (FTE) and Deutsche Telekom AG, will form a joint venture to help banks and advertisers access the service, which will let people buy items from groceries to clothes with a swipe of their smartphone, they said at the time.