LEEDS, England — Saying it has "fired the final shot in the supermarket price wars," Asda has launched an online lowest-price program in which the retailer vows to beat competitors’ prices.

Saying it has "fired the final shot in the supermarket price wars," Asda has launched an online lowest-price program in which the retailer vows to beat competitors’ prices.

Dubbed the Asda Price Guarantee, the effort provides "a cast-iron promise to shoppers" that Asda won’t be beaten on price, according to the United Kingdom grocery retailer, a subsidiary of Wal-Mart Stores Inc.

The program, kicked off Wednesday, covers more than 13,000 branded and own-brand products, as well as promotional items. If shoppers can buy eight or more comparable products cheaper elsewhere, Asda will give them the difference, "plus a penny more for good measure," said the retailer, which has 374 stores.

The Asda Price Guarantee works as follows: Customers making purchases at Asda keep the receipt and then after 9 a.m. the next day go to www.asda.com/priceguarantee to enter the receipt details to see how much that shopping trip would have cost at the other supermarkets. If customers could have paid less elsewhere, then Asda will give them a printable voucher for the difference plus one penny that can be redeemed against their next Asda purchase.

According to Asda, the program is the first time that a supermarket is using the Web to guarantee that its prices can’t be beaten. The price checker is built and powered by independent firm mysupermarket.co.uk, and it can be accessed by shoppers at www.asda.com.

"From today, Asda cannot and will not be beaten on price. Our grocery guarantee puts an end to the phony price wars that most shoppers are sick of. Plain and simple, our price guarantee is our cast-iron promise that your basket of shopping will always be cheapest at Asda," chief executive officer Andy Bond said in a statement.

"And for the millions of shoppers who go elsewhere, my challenge is this: Come to Asda this weekend and see for yourselves how much you’d save," Bond added.

Asda said it’s able to offer the price guarantee because most items bought by shoppers in its stores are identical to those available at rival supermarkets. The company said mysupermarket.co.uk will compare like-for-like branded or own-label groceries, which account for roughly 70% of all grocery sales at Asda.

"As an independent consumer champion, our aim is always to help shoppers compare prices across the supermarkets in a fair and comprehensive way, and to make sure they get the best value for money," commented Daniel King, chief commercial officer for mysupermarket.co.uk. "We are powering the Asda Price Guarantee web site to help shoppers continue to do this, and we will be running all the comparisons based on independently collected prices. U.K. shoppers now have more tools at their fingertips than ever before to help them make their money go further when it comes to their grocery shopping."

Asda noted that about 10% of its products are unique to the store and won’t be included in the price checker. Also, another 20% of items could be comparable but not without changes to strict trading standards regulations. For example, Asda Brand Pickled Onions, Asda Brand Frosted Flakes Cereal, Asda Brand Broccoli & Cauliflower Florets and Asda Brand Ardennes Pate can’t be included because of small differences in the size of packets, the retailer said.