Scientists claimed to have made a major breakthrough in overcoming opposition to stem cell research by creating human embryos which cannot develop into babies.

The so-called “ethical” embryos have been created by using an enzyme dubbed the “spark of life” which tricks human eggs into believing they have been fertilised even without the presence of sperm.

Stem cells from the embryos can turn into different kinds of tissue and scientists believe that with the right chemical cues they could produce replacement tissue for patients suffering degenerative brain illnesses such as Parkinson’s disease as well as heart damage.

Dr Karl Swann, of the University of Wales College of Medicine in Cardiff, tricked the eggs into dividing by injecting phospholipase C-zeta (PLC-zeta), an enzyme produced by sperm that he discovered two years ago, into an unfertilised female egg.

He said: “It’s the spark of life. It tricks the egg into thinking it has been fertilised.”

According to a report in New Scientist magazine, embryos created by the new procedure contain two sets of chromosomes from the mother, but none from the father and so are unable to develop into babies.

Proponents of the new technique say that allays the fears raised by pro-life campaigners opposed to stem cell research.

The tricked eggs divide for four or five days until they reach 50 to 100 cells, which is known as the “blastocyst” stage.

In theory, the blastocysts should yield stem cells which can then be used for scientific research.

Bob Lanza, the head of research at the cloning company Advanced Cell Technology in Worcester, Massachusetts, in the United States, hailed the discovery as a major one.

He said: “This could eliminate one of the main sources of ethical controversy in this research.”

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