A scientist involved in creating Dolly the cloned sheep has proposed using cloning and gene alteration to create babies free from hereditary diseases.
Professor Wilmut is proposing altering cells from early-stage embryos
Professor Ian Wilmut argues in a new book that cloning a 100-cell IVF embryo is not the same as cloning a human.
Professor Wilmut, of the Roslin Institute near Edinburgh, says it would be "immoral" not to use the promise of new technology to help families.
But opponents called the plan "unethical" and "utterly perverse".
Professor Wilmut describes how it would be possible to take an embryo affected by an hereditary disease and then remove its stem cells and modify the genetic fault which, left unchecked, would cause a condition such as Huntington's disease or cystic fibrosis .
These defect-free cells would then be cloned and used to create a new embryo which was not affected by disease.
This would then be implanted and allowed to develop into a baby.
'Drawing a line'
Professor Wilmut has in the past said he is "implacable opposed" to cloning a human being.
But in his book, After Dolly, which is being serialised in the Daily Telegraph, he argues that is not what he is now suggesting.
"An early embryo is not a person, and I see the use of cloning to prevent a child having a dreadful hereditary disease as far less controversial.
"I simply can't see anything immoral about the use of these methods to prevent disease and suffering."
Professor Wilmut says many moral, ethical and practical questions would be raised by the use of the technique, as well as arguments over where to "draw the line between eradicating the disease and enhancing a child".
He said it was "easy to understand" the desire to prevent the birth of a child with a serious genetic disease such as Huntington's, or to be able to administer a synthetic growth hormone to ensure a stunted child grows to a normal height.
But he questioned what would happen if couples wanted to have a tall child - because taller people have been shown to fare better in many areas of life.
Professor Wilmut writes: "Whatever the shades of grey between enhancement and therapy, I believe that society has an obligation to intervene on the embryo's behalf when it comes to weighing the risks and benefits of genetic alteration."
'Science without sense'
However, he said the technique did raise other issues.
Any such manipulation would not only affect the resulting child's genetic make-up, but also that of its own offspring.
And, if it was introduced, the technology would, at least initially, be very expensive, suggesting, Professor Wilmut says, there will be "genetic haves and have-nots".
The Human Fertilisation and Embryology Authority, which regulates any scientific work involving embryos, said the replacement of a cloned embryo into a woman would be banned under the Human Reproductive Cloning Act (2001).
Julia Millington, political director of the ProLife Alliance, said: "The quest for perfection knows no bounds.
"Selecting healthy cells from an embryo with genetic defects in order to clone it; thereby creating a healthy identical twin is not only unethical, it is utterly perverse."
Matthew O'Gorman, spokesman for the pro-life group LIFE, said: "What Professor Wilmut fails to mention is that the cloned embryos will be deliberately destroyed once they have provided useful genetic material.
"Such a proposal is abhorrent for it treats the embryo as an instrument rather than an individual.
"Embryos will be commanded into existence; cloned simply to service another which is a shameful example of science without sense."