Sainsbury's is undertaking a massive customer loyalty drive in a bid to increase its sales by £1bn, The Grocer can reveal.

The retailer has asked its staff to brainstorm ways in which it can get customers to keep returning to its stores. Staff will be awarded £100 in Shining Star vouchers in return for their ideas, which will also be nominated for Suggestion of the Year at the retailer's annual Star Awards for staff.

The supermarket chain said that of the 16.5 million customers it currently served every week, only 2.5 million exclusively shopped at Sainsbury's. There was an opportunity to boost this figure as well as average basket spend, it said.

"You meet them everyday and really know what they want, so we want you to tell us what we can do to keep our shoppers coming back, encourage them to shop with us every time, and see how we can get an extra £1.17 into their baskets," the retailer wrote in the latest edition of its staff magazine, Sainsbury's Journal.

If all 16.5 million of its customers spent an extra £1.17 per visit that would bag Sainsbury's more than £1bn extra a year in sales, which would provide a sizeable chunk of the £3.5bn sales growth it announced last month it hoped to achieve by 2010.

The initiative was tied in with Sainsbury's 'Try Something New Today' campaign launched in September 2005 to change the way customers shopped, said a spokeswoman, and was a key part of its Making Sainsbury's Great Again plan, which has generated an extra £2.7bn in sales since March 2005.

Meanwhile, Sainsbury's confirmed it was considering opening more temporary stores in the car parks of stores closed for refurbishment.

The move follows the success of a 5,000 sq ft Sainsbury's Local marquee in the car park of its New Barnet store in north London, which opened for three weeks while the main store was closed for refurbishment. In its first week, it beat sales estimates by more than 200%, serving 13,000 customers. "The temporary site was a success, and we may look to do it in the future, but there are no firm plans in place yet," a spokeswoman said.