"The advantage of 'high low' is the wow effect," says Ms Bain. "But 'every day low prices' is more of a loyalty-building, 'you can trust us' positioning."

Safeway has demonstrated another problem with "high low". While the number of customers visiting its stores is increasing, it reported sales towards the lower end of analysts' expectations at Christmas.

"At Safeway a lot of shoppers are cherry-picking, so they are only buying when it's 'low' and then buzzing off and buying somewhere else," says Mr Garner at Superpanel.
—Heather Tomlinson, "Every little helps Tesco keep its competitors at arm's length," The Independent, April 7, 2002