Campaigners expressed "extreme concern" today over claims milk from the offspring of a cloned cow was on sale in Britain.
The Food Standards Agency (FSA) is investigating reports that a British dairy farmer admitted using the milk, without labelling it as from a cloned cow, in his daily production.
Under European law, foodstuffs - including milk - produced from cloned animals must pass a safety evaluation and get approval before they are marketed.
But the FSA, the UK body responsible for the assessment of so-called novel foods produced by cloned animals and their offspring, said it has not made any authorisations nor been asked to do so.
The farmer, who wanted to remain anonymous because he feared consumers would stop buying his milk, made the claim to the International Herald Tribune.
He also said he was selling embryos from the same cow to breeders in Canada.
Peter Stevenson, from campaign group Compassion in World Farming, said he was "extremely concerned".
He said: "The Food Standards Agency must act quickly to trace this milk and get it withdrawn from shops. The cloning of farm animals can involve great suffering.
"A cloned embryo has to be implanted into a surrogate mother who carries it to birth. Cloned embryos tend to be large and can result in painful births that are often carried out by Caesarean section.
"Many clones die during pregnancy or birth. Of those that survive, a significant proportion die in the early days and weeks of life from problems such as heart, liver and kidney failure. The European Parliament has voted for a ban on the sale of meat and milk from clones and their offspring.
"We call on the coalition Government and the rest of the EU to follow the Parliament's lead and prohibit the sale of food from cloned animals and their offspring."
An FSA spokeswoman said: "Since 2007 the FSA interpretation of the law has been that meat and products from clones and their offspring are considered novel foods and would therefore need to be authorised before being placed on the market.
"As the UK authority responsible for accepting novel food applications, the agency has not received any applications relating to cloning and no authorisations have been made.
"The agency will, of course, investigate any reports of unauthorised novel foods entering the food chain."
Dr Brendan Curran, a geneticist at Queen Mary University of London, told Sky News: "A healthy animal will give you healthier milk.
"I'm less convinced of the ethics of it. I can see a good argument for animal welfare people being very concerned because it has to be done under really strict conditions and in a very compassionate way for the animal. But after the animal has been born and it has become an adult I don't see any problem - they reproduce normally, they do everything normally."
There was concern about calves born to cloned parents three years ago when it emerged a calf from a cloned cow was born on a British farm.
Dundee Paradise was said to have been born to a surrogate mother on a Midlands farm after she was flown into Britain as a frozen embryo.
Her mother was created in the US using cells from the ear of a champion dairy Holstein, according to reports.
Later that year, public outrage caused Dundee Paradise and her brother, Dundee Paratrooper, to be withdrawn from an auction but it is thought they went on sale privately instead.