UK online sales reached a new record in December while high street retail sales fell this Christmas, a new report from accountancy firm BDO revealed.December non-store sales jumped 31.1%, rising to growth of 55.7% in the week before Christmas.Traditional high street retail sales, on the other hand, dropped by 2.2% last month.Independent retail consultant Richard Hyman told the Financial Times that online purchases accounted for almost 20% of total retail sales - up 5% on 2012.Non-food online sales accounted for around a third of all Christmas sales.Like-for-like sales, excluding online trade, declined by as much as 6.7% in the week to December 22nd.BDO said a 3.5% increase in the week to December 29th failed to lift the overall performance in December, which was down 2.2% on the prior year."Following on from what was a solid month of trading in November, many retailers will have been left disappointed by a month of lacklustre consumer demand in the crucial Christmas trading period," BDO said in a statement. "Pent-up demand was expected to play a larger role as we moved closer to Christmas day but in reality it never fully took hold."Debenhams issued a profit warning last week after reporting weak trading despite aggressive discounting.However, strong trading came from fashion chain Next and department store rivals John Lewis and House of Fraser.Marks & Spencer, which also cut prices in the run up to Christmas to attract shoppers, is due to report on Thursday, when the retailer is expected to reveal a challenging season.RD