Sainsbury's is considering launching a price-matching voucher scheme to rival Asda's Price Guarantee and Tesco's Price Check.

The supermarket chain has been canvassing opinion via a survey on whether shoppers would welcome a scheme that gave them a voucher for the difference at the till if certain products they bought were more ­expensive than at Asda, Tesco and Morrisons.

It is understood the scheme would be operated through the retailer's 'coupon at till' technology, which rewards Nectar card holders with vouchers printed at the checkout based on their own shopping habits. It would therefore be unique in offering shoppers an instant voucher. Currently, shoppers have to log onto a website to check whether they can claim vouchers from Asda and Tesco.

Sainsbury's research also suggests it would seek to avoid the mistakes made by Asda and Tesco when they introduced high-profile price pledges earlier this year.

Its survey asked shoppers' views on a number of possible restrictions to any scheme it might introduce, including limiting it to branded products, excluding beers, wines and spirits, restricting the scheme to just Nectar card holders and restricting the maximum value of vouchers.

Asda was initially rapped over the lack of clarity in the advertising of its scheme while Tesco was hit by shoppers exploiting loopholes in its promise to make money. In April, Tesco had to cut back its pledge to refund double the difference on products bought for less at Asda after it claimed a "cottage industry of savvy and determined people" were misusing the promotion.

"We're always looking at and researching different ways to offer customers the best possible value but have no immediate plans with this. We already check 30,000 competitor prices each week so our customers know we are working hard," said a Sainsbury's spokesman.

Shoppers on the website MoneySavingExpert.com have welcomed Sainsbury's plans. "Comparing against more than one supermarket is a plus compared to the others," said one.

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