Marks & Spencer has come under fire for abandoning its policy of selling only GM-free food.

The store is selling six products containing genetically-modified soya or corn despite having long presented itself as being opposed to such engineered products.

The six are teriyaki, ginger and hibachi sauces from the American TonTon brand, and three flavours of Moravian Cookie – sugar, chocolate, and cranberry and orange.

Marks & Spencer is selling six products containing genetically-modified soya or corn despite having long presented itself as being opposed to such engineered products

Other stores are also selling an increasing number of imported American foods from brands including Reese, Hershey and Oreo that contain GM ingredients.

The move has been condemned by critics of the technology who say it is evidence of the insidious way so-called Frankenstein foods are being introduced.

Last year, M&S, Tesco, Sainsbury’s and the Co-op abandoned pledges to ensure animals supplying milk, eggs, chicken, pork and beef were not fed a GM diet.

It means some food on supermarket shelves comes from animals fed on GM crops, without this fact being declared on the label.

Three flavours of Moravian Cookie, which contain GM ingredients, are being sold at Marks & Spencer

M&S and Tesco have a policy not to use GM ingredients in their own-label products, but it is now clear there are no such assurances for other brands. The TonTon sauce is the first GM food allowed on to M&S shelves, while Tesco has gradually started to sell these products.

There was a row last year when it emerged Tesco was stocking American Lucky Charms cereal, which is made from GM corn – a fact buried in small print on the package – and contains artificial colours that the Food Standards Agency has linked to hyperactivity in young children. But a free trade treaty that is being negotiated between the EU and the US is set to further open the door to American GM foods.

Dr Helen Wallace, of the research group GeneWatch, said the growing of GM soya and maize used in the teriyaki sauce sold by M&S has had a devastating impact on butterflies.

She said: ‘By importing this product, M&S is contributing to the devastating crash in Monarch butterfly populations. Weedkiller on GM soya and maize has destroyed vast swathes of the habitat. Customers are likely to be shocked by this cavalier disregard for the environment.’

Liz O’Neill, of campaigners GM Freeze, added: ‘People expect to be able to trust their favourite retailers, who wouldn’t put these ingredients in their own brand products.’

M&S said: ‘This is a very small number of products. They are clearly not M&S-branded products and are clearly labelled.

‘This in no way affects our commitment to only using non-GM food ingredients in M&S food.’

A Tesco spokesman said: ‘Our American range is very popular. All products are clearly labelled in line with relevant legislation.’