UK scientists have won permission to create a human embryo that will have three parents, charting new territory in the controversy over "designer babies"

The ground-breaking work aims to prevent mothers from passing certain genetic diseases on to their unborn babies and will create an embryo that has genetic material from two mothers and a father.

Such diseases, which are known as mitochondrial, arise from DNA found outside the nucleus and thus inherited separately from DNA in the nucleus.

A team from Newcastle University will transfer the pro-nuclei - the components of a nucleus of a human embryo - which have been made by one man and woman into an unfertilised egg from another woman.

A spokesman for the Human Fertilisation and Embryology Authority said in a statement: "The HFEA has today granted a licence to the Newcastle Fertility Centre at LIFE for the use of embryos for research into mitochondrial disease."

The application to carry out the research was initially rejected by the HFEA, but that decision was reversed on appeal after hearing expert evidence from leading geneticists.

The licence allows only experimental use of the technique and not the implantation of any embryo created into a woman’s womb.

Mitochondria are small complex structures which exist in every cell of the body, except red blood cells. They are the "powerhouse" of the cell, producing most of the energy required to grow and live, and they have their own DNA, which is inherited from only the mother.

If this DNA is faulty, mitochondrial diseases occur. At present no treatment for mitochondrial diseases exists. Organs in the body which require high energy to work properly, such as the brain, heart and kidney, are particularly dependent on well functioning mitochondria.

Studies in mice show it is possible to prevent the transmission of mitochondrial disease by moving the nucleus from an egg containing bad mitochondria to another egg, which only contains good mitochondria.

Professor Doug Turnbull, professor of neurology at Newcastle University, and Dr Mary Herbert, scientific director of Newcastle Fertility Centre at the city’s Centre for Life, now plan to do the same in humans.

Their UK research, permitted by the Human Fertilisation and Embryology Authority and funded by the Muscular Dystrophy Campaign, will check that transplanting the nucleus works and is safe.

Although the resulting egg would never be allowed to develop into a baby, if it did the offspring would still resemble their mother and father because the mitochondrial DNA do not dictate things such as hair colour. About one in 5,000 children and adults are at risk of developing a mitochondrial disease.

The Newcastle plan involves fertilising an egg in-vitro from a woman carrying mitochondrial defects, using her partner’s sperm. At the point of fertilisation, two "pro-nuclei" containing genetic material from the mother and father will be removed, and injected into an unfertilised egg from which the nucleus has been removed.

This donated egg will contain healthy mitochondria, but none of the nuclear DNA that makes up the vast majority of the human genetic code.

Mitochondria, however, do contain 37 genes, meaning that the embryo will have been created with a genetic contribution from three individuals: the father, the mother who provided the nucleus, and the donor who provided the mitochondria.

The procedure is not cloning, as the embryo that develops as a result will have a full complement of genes in its nucleus from both a mother and a father.

Clones created by nuclear transfer are genetically identical to the adult they are cloned from, with the exception of their mitochondrial DNA.

In May it was announced that scientists at Newcastle University had cloned a human embryo for the first time in Britain. They hope the work it will eventually lead to successful treatments for degenerative diseases such as Parkinson’s and Alzheimer’s, or for the paralysed victims of spinal injuries.

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