The boss of Asda has described his "shock" as revelations of the horsemeat contamination scandal broke and vowed to leave "no stone unturned" to address problems in the supply chain.
Andy Clarke, chief executive of the UK's second biggest supermarket chain, admitted trust among consumers had been dented, but said his solution would be a "belt and braces" approach to labelling to restore confidence.
He said: "We weren't on our own to be shocked by what came out six weeks ago. For us as a business, the first thing we did was look inside our own organisation to identify if we had anything we should be concerned about."
Asda has withdrawn two products from sale, an own-brand bolognese sauce and Freeza frozen beefburgers.
Mr Clarke said: "Right from the start we took a very transparent approach and, of course, embarked on what is a world-leading change for the industry and our organisation in terms of testing. What is clear is that there is significant adulteration in the supply chain.
"For Asda, at the end of the day, our customers come into our stores and they expect to buy what's on the label. So I feel very responsible for that, but I want you to know that I'm leaving no stone unturned to address what happened in our supply chain."
Asda reported like-for-like sales, excluding petrol, grew 0.1% in the 14 weeks to January 5. For the full year, like-for-like sales increased by 1%, excluding petrol.
Mr Clarke said: "We're pleased with our results in a tough market. We continued to grow our sales while also investing in holding down the price of essentials, increasing access points to Asda's value and putting money back in customers' pockets when they need it the most.
"Our multichannel, George and general merchandise are all performing well. We have seen online clothing sales growing faster than the market, with our biggest Christmas ever.
"But this is no time to be complacent. It's likely to be a challenging and uncertain year ahead and so we will continue to focus on the customer and adapt the business to their needs. By doing this, I'm confident we have a strong business that can drive growth in a sustainable way."