Is horse meat still on sale in Britain? The scale of the company's trade with Britain prompted concerns that more contaminated meat may be on sale in supermarkets. Barry Gardiner, a Labour member of the environment select committee, accused the Food Standards Agency of failing to investigate properly. He said the FSA had to "get it back together and go right the way through the suppliers and make sure they know what's in the food people are eating." Mr Gardiner added: "The FSA has been happy to let other people do the work they should be focusing on. They must be proactive and not leave it to someone else. Food Service, based in central Poland, processes up to 15 tons of beef every day and exports it all over the world. It also slaughters pigs and processes pork products. The company, which has a £60 million turnover, has its own cold storage facility and a fleet of lorries to transport the meat to other countries. It was audited to standards set by the British Retail Consortium in May 2012 and given a food safety certificate of approval. Food Service supplied 20 tons of beef a month to Silvercrest. Last week the Food Safety Authority of Ireland identified the company as its prime suspect in the hunt for the supplier of contaminated beef on sale in British supermarkets. It contacted the authorities in Poland, who conducted a series of DNA tests at the site on its current stock and five of the slaughterhouses that supply it. On Friday the Polish authorities said that all the tests had come back negative and suggested the source of the contamination may be in Ireland or England. Jaroslaw Naza, the deputy head of Poland's general veterinary inspectorate, said: "Everything we have done suggests to us that the source of the contamination was not in Poland. How has this happened? Someone probably changed documents. I know that the authorities in Ireland are looking for changes of labelling and documents. Maybe it is in England? Mr Czerniej - who runs Food Service with its co-founder Zofia Sypula - insisted the company was not the source of the contamination. He said: "We have never bought or handled horse meat, we couldn't have been the source of contamination. [Our] beef is subject to rigorous procedures and identification. We supply six companies in Britain with beef. I can't tell you who because that is a company secret. We sell meat to hamburger producers but what happens in the end to the hamburgers, I don't know. A spokesman from the Irish agriculture department insisted on Friday that "evidence shows the origin of the product to come from Poland." The investigation in Ireland last month found Tesco was selling hamburgers that contained up to 29 per cent horse meat. Seven supermarkets pulled millions of frozen burgers from their shelves amid fears of more widespread contamination. The FSA is planning a series of DNA tests to identify if other beef has been contaminated. A spokesman for the agency said it was making "strenuous" efforts to find the cause of the contamination. She added: "We are working directly with the Polish authorities to track exactly where products from the manufacturer in Poland have been sent, and by which suppliers they have been received in the UK. We take this extremely seriously as consumers must be able to have confidence that the food they consume is correctly described. We are in the process of carrying out a complex and technical investigation and will ensure that we keep consumers up to date.