In a letter seen by the Sunday Times to the Commons science and technology committee, which is holding a one-day inquiry into three parent embryos on October 22, a group of scientists said: "The safety of mitochondrial replacement therapy is not yet established sufficiently well to proceed to clinical trials."

However, an editorial in New Scientist said mitochondria "play a key role in some of the most important features of human life. This raises the ethically troubling prospect ... that children conceived in this way will inherit vital traits from three parents."

Stuart Newman, a cell biologist and professor at New York Medical College, will submit his objections this week and said the importance of the outer part of the egg, donated by the second woman, was being played down.

"The mitochondria are ... participants in the development of the organism. This clearly makes any person [brought into being from the procedure] a product of wholesale genetic engineering," he said.

The Human Fertilisation and Embryology Authority, which backs mitochondrial replacement, said it could "see no reason for changing its in-depth and considered views on this matter".

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Three-parent babies are 'genetic engineering' and be banned