Asda reported strong Christmas trading in both store and online, hailing its strategy for boosting sales during the season.Ahead of its fourth-quarter results in February, the British arm of US grocer Wal-Mart Stores on Monday revealed that it enjoyed a good performance last month."Our strategy was to focus on gimmick-free, simple every day low price transparency for our customers and to hold our nerve when it came to the sales," it said."This was against the backdrop of many other retailers vouchering heavily and starting their sales early, and resulted in us seeing record footfall over the Christmas period."The supermarket is battling with J Sainsbury to be Britain's second-largest grocer after Tesco. Sainsbury will report third-quarter sales on Wednesday, while Tesco will update on the six weeks to January 4th on Thursday.RD