The technique is intended to help women with diseases of the mitochondria - mini organelles that are found within individual cells.

They are sometimes described as "cellular power plants" because they generate most of the cell's energy.

Faults in the mitochondrial DNA can cause around 50 known diseases, some of which lead to disability and death.

About one in every 6,500 people is affected by such conditions, which include fatal liver failure, stroke-like episodes, blindness, muscular dystrophy, diabetes and deafness.

At present, no treatment for mitochondrial diseases exists.

Genetic transplant

The Newcastle team have effectively given the embryos a mitochondria transplant.

They experimented on 10 severely abnormal embryos left over from traditional fertility treatment.

Within hours of their creation, the nucleus, containing DNA from the mother and father, was removed from the embryo, and implanted into a donor egg whose DNA had been largely removed.

The only genetic information remaining from the donor egg was the tiny bit that controls production of mitochondria - around 16,000 of the 3billion component parts that make up the human genome.

The embryos then began to develop normally, but were destroyed within six days.

Appearance

Experiments using mice have shown that the offspring with the new mitochondria carry no information that defines any human attributes.