Asda chief executive Andy Clarke has vowed to “leave no stone unturned” in the hunt to discover the extent of meat contamination in the supply chain following the horse meat scandal.

The grocery boss said that horse meat found in processed beef products in Asda and its competitors had “dented trust” from consumers and that he is monitoring the results of tests on beef products every day.

Clarke said Asda is combing its supply chain for answers as to how horse meat entered the chain and is “getting ahead of the game” in testing other products before required to by the Food Standards Agency.

He said: “Our customers expect to buy what’s on the label. In one case for us that was not the case. I feel very responsible for that, I am the chief executive and I will leave no stone unturned. We will get to the bottom of it and resolve it because that’s the way we do business.”

The grocer has seen consumer habits change as a result of the crisis. “Consumers are switching to veggie meals and meat-free products have taken a lift. In overall terms there’s been a small impact,” said Clarke who stressed “this is not a food safety issue it’s a labeling challenge”.

Clarke declined to put a figure on the investment Asda is making in the expensive testing process which Tesco said it was spending £1m on. He said each test costs £500.

His comments came after The Co-operative Group chief executive Peter Marks today apologised to customers for its part in the horse meat scandal. Sainsbury’s said today it has tested 250 own label beef products and found no horse meat.

Aldi joint managing directors Matthew Barnes and Roman Heini said in an email to customers today. “We let you down and we’re sorry”. They blamed “certain suppliers who did not comply with the standards we set”.

Clarke spoke as Asda revealed full-year like-for-likes edged up 1% while like-for-like sales in the 14 weeks ending January 5, increased 0.1% today.

Asda chief financial officer Richard Mayfield said he expects Tesco to hit back with new promotions following the end of its financial year this month.

He said: “Tesco has been pretty quiet so far, we are expecting that to change. Towards the end of last year Sainsbury’s was less active and Tesco was getting more into use of Clubcard and that’s a more targeted investment I suppose. Customers like simple and large discounts.”