Jan 17 (Reuters) - Booker Group Plc, Britain's biggest cash-and-carry wholesaler, reported a rise in sales in the 16 weeks to Jan. 4, helped by demand from small businesses. The company, which runs more than 170 branches supplying caterers, convenience stores, grocers, restaurants and pubs, said like-for-like sales were up 3.1 percent during the period. Booker has defied the downturn in the sector, managing to grow sales as Britons increasingly shop at their local convenience store instead of supermarkets.