“Meat free” and vegan food sold at Britain's leading supermarkets contains traces of meat, an investigation by the Daily Telegraph can disclose.

Laboratory tests found traces of pork in Sainsbury’s own brand “meat free” meatballs and traces of turkey in a vegan macaroni ready meal from Tesco’s new “Wicked Kitchen” line.

Friday night the Food Standards Agency said it was investigating this newspaper's findings. Jewish and Muslim groups warned consumers would be "distressed" to discover they may have inadvertently eaten pork, and demanded the affected items be recalled.

It comes as supermarkets rush to expand their meat free ranges with 3.5 million people now identifying as vegan or vegetarian in the UK.

The product from Sainsbury's has been awarded the Vegetarian Society logo, which is highly trusted by vegans and vegetarians as it is thought to show that products have been subject to strict controls including preventing cross contamination with animal products.

Tesco has admitted that the dish from its Wicked Kitchen range, which launched in January, is made in a factory which handles meat, claiming "strict controls" are in place.

The presence of whole animal DNA indicates that a dish contains meat or animal skin, the lab said, with an outside chance it could be present in gelatine or oil - substances which should not be present in vegan dishes.