LONDON (Reuters) - Britain's biggest department store group John Lewis said on Sunday its sales grew by 2.1 percent to 112 million pounds ($181 million) in the week to November 23, helped by cold weather boosting outerwear purchases. Online sales grew 9.4 percent compared with the previous year. Overall sales grew 10.3 percent compared with the previous week, with the new iPad Air being the best selling gift for the third week in a row. Maggie Porteous, director of selling operations, said that this week's comparatives with last year were tough because "Black Friday", the day in the run up to Christmas when retailers offer deals and discounts to attract shoppers, falls in a different week this year. The 149-year-old firm has been winning share from high-street rivals in recent years due to its strong online offering, modern stores and a more affluent customer base. Last Christmas it reported record sales, while rivals, such as Marks & Spencer (M&S) endured poor trading in a tough market. (Reporting By Christine Murray; Editing by Ruth Pitchford)