British supermarket giant J Sainsbury is expected to unveil plans for new flexible store formats this week, in a bid to enable stores to adapt itself to the particular requirements of "clusters" of shoppers. The retailer, which ranks as the second-biggest supermarket group in the UK, has reportedly developed the new flexible formats in an attempt to boost efficiency; stock levels can be altered to reflect different tastes in the area, or to better suit the stores at which more families shop regularly. Two stores recently refurbished with the new format are due to open this week, and if they prove successful, Sainsbury will be rolling out the changes across its chain.