A debate over produce from cloned animals has been sparked in the UK after the country's food watchdog said meat from the offspring of a cloned cow had entered the food chain and been eaten.
The Food Standards Agency (FSA) carried out an investigation into the produce after media reports earlier this week said milk from a cow produced from a cloned parent was sold in Britain.
The watchdog said on Wednesday that while there was no evidence that such meat could pose a health risk, products from cloned animals are considered "novel foods" and cannot be marketed unless authorised.
Under European rules, suppliers of meat linked to cloned animals must obtain a licence before selling their products.
Some food campaigners have raised questions over the ethics and safety of allowing produce from cloned animals into the market.
"Cloning involves applying invasive and cruel techniques on the surrogate mothers that are used for producing the clones," Emma Hockridge, head of policy at the Soil Association, said.
She said cloning also raised worries about the safety of meat and dairy products and the spread of diseases, "as well as concerns about the ethics of cloning".
But Brendan Curran, a geneticist from Queen Mary, University of London, said tests by the US Food and Drug Administration (FDA) had found no evidence that meat and milk from cloned animals or their offspring was any different from traditionally reproduced livestock.
"They have concluded therefore that it is safe for humans to consume produce from such animals," he said.
"There is no reason why the situation should be any different in the UK."
The FSA said it had identified two bulls born in the UK from embryos harvested from a cloned cow in the United States.
One of the bulls, known as Dundee Paratrooper, was slaughtered in July 2009, and its meat entered the food chain and "will have been eaten," the agency said.
The other bull, called Dundee Perfect, was slaughtered on July 27, but officials stopped its meat from entering the food chain, the FSA said.
The FDA approved the sale of food from clones and their offspring in 2008, stating the products were indistinguishable from those of non-cloned animals.
The European parliament recently voted to exclude food from cloned animals from a list of approved products.
A "novel food" application must now be made before it can be sold.