MPs will vote today on the divisive issue of "three-parent babies", in which a couple uses the DNA of a second woman to repair genetic faults in an unborn child.
The technique would help about 150 couples a year, where there is a risk of the mother passing down defective mitochondria – tiny compartments inside nearly every cell in the body – which can lead to brain damage, muscle wasting, heart failure and blindness.
A modified version of IVF combines the DNA of two parents with the healthy mitochondria of a second donor woman, producing a baby with 0.1 per cent of its DNA from the third parent.
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If the amendments to the Human Fertilisation and Embryology Act 2008 go through, Britain will become the first country in the world to permit three-parent babies, the first of whom could be born as early as next year, says the BBC.
But the vote, which is due to take place this afternoon, has already sparked a fierce moral and medical debate, as the genetic change will be passed on through generations, with any unexpected issues affecting people who are not yet born.
The Catholic Church and the Church of England have raised ethical and medical concerns, urging politicians not to rush into the decision.
But a number of leading scientists, including five Nobel laureates, called on MPs to support the legislation. In a letter to The Times, they wrote: "We believe that those who know what it is like to care for, and sometimes to lose, an extremely sick child are the people best placed to decide whether this technology is right for them, with medical advice and within the strict regulatory framework proposed. They have been waiting for the science for long enough. They should not have to wait for the law to catch up."
Signatories included Sir Paul Nurse, president of the Royal Society; Sir John Gurdon, who won the 2012 Nobel Prize in physiology or medicine; and the Rt Rev Lord Harries, a former bishop of Oxford.
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