British supermarket chain Sainsbury\'s said on Wednesday that sales grew during the crucial Christmas and New Year trading period. Sales from stores open at least a year, excluding petrol, increased by 2.1 percent in the 14 weeks to January 7, compared with the same part of the previous financial year, Sainbury\'s said in a third-quarter trading statement. Customer transactions in the week before Christmas increased by 1.5 million to a record 26 million. \"This was a strong quarter, rounded off by our best Christmas ever, despite the economic backdrop,\" Chief Executive Justin King said in the statement. However, the group warned that shoppers would remain cautious at the start of this year -- but predicted growth \"opportunities\" driven by the London Olympics and celebrations marking 60 years of the queen\'s reign. \"Consistent with trends over the past year, we expect customers to spend cautiously in 2012, particularly in the first few months as they tighten their belts post Christmas,\" Sainsbury\'s said. \"Although the short term remains challenging, key events later in the year, such as the Queen\'s Diamond Jubilee and London 2012 Olympic and Paralympic Games, provide opportunities for growth. \"We will continue to invest in our offer to support our customers through these difficult times.\" Sainsbury\'s is the third-biggest supermarket chain in Britain after Wal-Mart owned Asda and the country\'s biggest retailer Tesco.