The Food Standards Agency (FSA) has said it is unsure how many embryos from cloned cattle have been imported into Britain, after admissions that meat from the offspring of a cloned cow has been purchased and probably eaten.
The FSA also says it is continuing with the investigation into claims that milk from a cloned cow's offspring had ended up on sale in Britain.
BBC News looks deeper at the reports and at the issues surrounding meat and milk from cloned animals.
Is it legal to sell meat from cloned cattle or their offspring in the UK?
According to the FSA, milk and meat from cloned animals are considered "novel foods" and suppliers have to get a special authorisation before selling them.
"While there is no evidence that consuming products from healthy clones, or their offspring, poses a food safety risk, meat and products from (them) are considered novel foods and would therefore need to be authorised before being placed on the market," the FSA said.
But since there are no restrictions on importing semen from a cloned animal, some newspaper reports claim there could be thousands of cattle in the EU that were born from clones.
Professor Grahame Bulfield, former director of the Roslin Institute where Dolly the sheep was cloned, said that he was surprised by the FSA's rules.
"The FSA is just making itself very foolish - especially now it is following up offspring of offspring of clones," he said.
"The FSA cannot produce any evidence that meat from clones or their offspring is novel in any way, or is any different to other meat. There is none, because it must be exactly the same."
The sale of food from clones and their offspring is legal in America. The US Food and Drug Administration (FDA) in 2008 stated that such products were indistinguishable from those of non-cloned animals.
How did the FSA trace the meat from a cloned cow?
The FSA said that during its investigation into the reports that milk from the offspring of a cloned cow had been sold, it traced two bulls born in Britain back to embryos harvested from a cow in the US. The cow was cloned five years ago.
One of the bulls in question, Dundee Paratrooper, was slaughtered in July 2009 and its meat entered the food chain, the agency added.
The second bull, Dundee Perfect, was born in March 2007 and was slaughtered just a few days ago, on 27 July. Its meat has been intercepted before entering the food chain.
What about the milk?
The FSA has said it is still trying to find out whether or not milk from the offspring of a cloned cow was at any point sold in the UK.
The agency said it had traced a cow called Dundee Paradise, which is believed to be the offspring of a cloned animal. But the FSA said it was too early to confirm that milk from this animal had entered the food chain.
Earlier, The New York Times reported that a British dairy farmer, who wished to remain anonymous, was selling milk from the offspring of a cloned cow.
He did not want to disclose his identity, the newspaper said, because "the British public regarded cloning as so distasteful that buyers would stop taking his milk…[and] he did not want to be required to get rid of a valuable cow." The paper also reported that the farmer was selling embryos from the same cow to breeders in Canada.
Is it safe to consume milk and meat from cloned animals and their offspring?
According to a research paper published by scientists in the US and Japan in 2005, milk and meat from cloned cattle appear safe for consumption.
The team, led by Jerry Yang from the University of Connecticut, compared the produce from two beef and four dairy clones with that from normal animals of similar ages and breeds.
The scientists found that the cloned cow meat was slightly higher in fat and fatty acids, but still within beef industry standards. Other than that, there were no significant differences, and produce from cloned cattle was said to be safe to eat and drink.
Dr Brendan Curran, a geneticist from the school of biological and chemical sciences at Queen Mary, University of London, said cloning was "an extension of the process by which identical twins arise in nature".
"Therefore if you have a healthy cow that is producing milk, it will produce healthy milk. I would argue that once the animal has been certified by veterinary surgeons as a fit animal, I can't see how it would be in any way dangerous."
The US' Food and Drug Administration has a similar opinion.
It has concluded, based on the results of a number of studies, that "meat and milk from clones of cattle, swine (pigs), and goats, and the offspring of clones from any species traditionally consumed as food, are as safe to eat as food from conventionally bred animals".
But some disagree.
Pamela Brunton, policy adviser for the Soil Association, said: "The research into the health and safety of meat and milk from cloned animals is entirely insufficient. There are very few peer-reviewed studies out there that investigate this in depth. The three studies that do exist do seem to show a difference in the composition of meat and dairy products."
What is a clone?
A clone is a genetic copy of an animal. Scientists say that clones are similar to identical twins, but born at different times.
Animal cloning has been around for more than two decades. The first mammal cloned from the cell of an adult animal was Dolly the sheep, born in 1996. She died in February 2003.
Most cloning nowadays is carried out using somatic cell nuclear transfer:
- Scientists remove the gene-containing nucleus from an egg taken from a female animal
- They then add to the egg the nucleus of a cell from an animal they wish to clone
- The egg cell begins to form into an embryo in the laboratory
- The embryo is then implanted in the uterus of a host animal which carries it to term and delivers it like her own offspring
According to the Genetic Science Learning Centre of the University of Utah, the success rate ranges from 0.1% to 3%. That means that only one to 30 clones are made for every 1,000 attempts.
Are cloned animals generally normal and healthy?
It has been shown that animals conceived through an assisted reproductive technique have a higher risk of neo-natal death.
Those clones that do survive are often much bigger at birth than animals born in a natural way. They can have abnormally large organs, which can lead to a number of problems, sometimes with breathing and blood flow. This is known as "Large Offspring Syndrome" (LOS).
Peter Stevenson, from Compassion in World Farming, said that the cloning of cattle for food should not be allowed.
"We're very disturbed. We now need urgent action. We need the governments in Scotland and Westminster to take the lead in persuading the European Union to ban the cloning of animals for food. And I say this because of the great animal suffering involved in cloning."
But Dr Curran from the school of biological and chemical sciences at Queen Mary, University of London, does not agree.
"I could see an argument for the animal welfare people being concerned, but since these procedures have to be done under very strict conditions and in a compassionate way for the animal, this also shouldn't be a problem," he said.
"After the animal has been born and grows to be an adult, it reproduces normally and does everything normally."