Helen Dickinson, the new director general of the BRC, said the "stand-out" online performance came after slower momentum in the previous few months.
She said: "Many valued the ease and convenience of shopping online during the Christmas period. The surging popularity of tablets and smartphones giving even better access is a major factor."
She also said shoppers felt much more comfortable putting their credit card details into their mobile phones.
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Misty low cloud and some patchy fog again tonight but with mild air