The clones are the genetic replicas of Dolly the sheep
Four clones of Dolly the sheep, the world's first mammal to be cloned from an adult cell, are alive and well and living in Nottinghamshire.
University of Nottingham researchers created the quads three-and-a-half years ago from the same genetic material used to make Dolly.
The sheep are being used carry out further research into cloned animals' longevity and susceptibility to disease.
Professor Keith Campbell, leading the research into animal development, was part of the team that created Dolly.
Dolly was "euthanised" at the age of six after suffering from arthritis and contracting lung disease, but Prof Campbell said the new clones showed "no signs" of similar health problems.
As sheep can live up to 12 years of age, her relatively early death sparked debate about the ethics of cloning.
The existence of the clones, known to researchers as "the Dollys", came to light earlier this month after Prof Campbell took part in a discussion on cloning at the European Parliament in Strasbourg.
He has been working on animal improvement, and cloning in particular, at the University of Nottingham since 1999.
He said a lot had been learnt about the cloning process since the creation of Dolly.
"For several years we worked on ways of improving technology and understanding it," he said.
"Using that information we've been able to modify techniques.
"[We created] the clones from Dolly when we thought we'd made improvements."
Prof Campbell said the aims of his work are numerous.
"[Cloning] has great implications for human development, animal development and for stem cells," he said.
"Agriculture is only one of the options. We can preserve genetics of farm animals especially rare breeds that we are losing."
But Professor Campbell added he believes "we would never be eating cloned animals".
The four sheep are now living "the life of Reilly" as "normal, healthy pets" on university land, according to Prof Campbell.
DOLLY THE SHEEP
Dolly was the first mammal to be cloned from an adult sheep rather than an embryo
Dolly was created on 5 July 1996 but the Roslin Institute waited until 1997 to announce her creation
Dolly was named after country singer Dolly Parton because she was cloned from a breast cell
Dolly has been preserved and is now on display at the National Museum of Scotland
The announcement of Dolly's creation in 1997 was deemed one of the most significant scientific breakthroughs of the decade.
Dolly bred naturally twice, giving birth to Bonnie in April 1998 and three more lambs in 1999.
In 2003, a decision to "put down" six-year-old Dolly was made after a veterinary examination showed she had a progressive lung disease.
The long-term health of clones is still debated by scientists but there is no proof that Dolly died because she was a clone.
Professor Campbell said: "Dolly died of a viral lung disease which is very common in sheep which are housed and share water.
"It causes lots of mucus production which then passes into water and gets drunk by the next sheep so [gets passed on]."
"Many, many clones [since Dolly] have lived normal lives and lived to good ages of 10 or 11 years old or more," he added.