Routine tests on cans of tomatoes sold under the Asda, Princes, Safeway and Tesco brand names showed levels of tin, which can cause vomiting and diarrhoea, exceeded statutory safety limits
The Ministry of Agriculture, Fisheries and Food (Maff) said affected batches had been removed from supermarket shelves and urged customers who had recently bought tinned tomatoes to contact their retailer.
Jeff Rooker, the Food Safety minister, sought to reassure the public by saying the food industry had taken a responsible attitude. "We are putting the information in the public domain, in line with Maff's commitment to openness and transparency in every area of our food safety work," Mr Rooker said.
Maff, however, refused to say whether it knew the name of the canning factory that supplied the contaminated tomatoes or whether it had asked the supermarkets to name their suppliers.
Steel food cans are lined with a thin layer of tin because the metal does not corrode. A Maff spokesman said that in some batches the average level of tin found in the tomatoes was 279 milligrams per kilogram, with one tin registering 293 mg/kg. The statutory limit is 200 mg/kg.
The problem came to light at the end of last month when Safeway alerted Maff to the results of tests it had done on its own brand of tinned tomatoes.
Maff's Joint Food Safety and Standards Group issued a warning to environmental health officers whose own tests showed the problem was more widespread.
"Maff will carry out an extensive survey of tin in canned tomato products to obtain further information on the extent of the problem. The results of the survey, including the brand names of products tested, will be made publicly available," Maff said last night.
Safeway said it was alerted to the problem a month ago when it identified tin levels above the approved limits in its 400g own-brand cans. It removed the products from the shelves and put up posters in all its 473 stores asking customers to return them.
The company said yesterday that it was a "purely precautionary measure".
Asda, which has 223 stores, withdrew tins of all its 400g Asda hand-picked plum tomatoes on Wednesday after Maff tests revealed one batch contained levels of tin above the 200mg limit. "Further testing failed to replicate those results. But as a responsible retailer we withdrew the product from stores when we found out as a precautionary measure," an Asda spokesman said.Reuse content