The NFU has called on the public to help stamp out misleading food labelling by taking pictures of products on shop shelves and uploading them to Facebook.
Research commissioned by the union for its "Flag It" campaign found that several retailers had been flouting DEFRA's voluntary code on country of origin labelling on some imported cheese and dairy products.
The research also showed that 83% of shoppers thought country of origin labelling on milk in dairy products should be clearer.
NFU director of corporate affairs Tom Hind said: "While genuine improvements have been made in labelling over the past few years, there are still examples where labels on many products are not clear and can confuse consumers into thinking they are buying British produce when they are not.
"So the idea behind the Flag It campaign is to get as many retailers as possible to ensure that labelling, especially on own-brand products, is crystal clear, so consumers know what they are getting."
Mr Hind added: "We are really pleased to have been able to work collaboratively with Tesco in the development of a new label for its Everyday Value cheddar cheese, and we hope that other retailers will ensure labels provide clear information for customers.
"That's why we want the public to be alert and let us know when packaging on products is unclear, so we can highlight these to the retailer and ask for it to be changed. Simple clarity on products will ensure people can buy exactly what they want every time they go to the supermarket to do their weekly shop."
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For more on labelling, see our report on Livestock 2012