FERTILITY doctors in Newcastle are a short step away from creating a "three-parent" baby to prevent inherited disease.

Regulators said the Newcastle Fertility Centre at Life had crossed the first hurdle in the two-stage process of obtaining a licence to carry out the IVF treatment.

Approval of the clinic's facilities, equipment and staff was announced by the Human Fertilisation and Embryology Authority (HFEA), which polices fertility treatment and research.

A separate appraisal of the suitability of the first patient selected to undergo the therapy will now be made by the HFEA.

This will take account of medical history and personal biology to ensure that the procedure is safe and likely to meet with success.

Once the patient has been cleared, a licence to carry out the treatment will be granted, probably before the end of the year.

A source said: "Every patient application has to be considered separately and they have to be very careful."

The aim of the treatment is to prevent women passing on defective genes in the mitochondria - tiny rod-like power plants in cells which supply energy.

But the technique, which involves giving a woman an IVF baby with DNA from three individuals, is highly controversial.

The baby will have nuclear DNA from its mother and father which define key characteristics such as personality and eye colour.

In addition, it will have a tiny amount of mitochondrial DNA provided by a female donor - the third "parent".

HFEA chairwoman Sally Cheshire, who announced the news at the regulator's annual meeting in London, said: "This significant decision represents the culmination of many years' hard work by researchers, clinical experts and regulators, who collectively paved the way for Parliament to change the law in 2015 to permit the use of such techniques.

"Patients will now be able to apply individually to the HFEA to undergo mitochondrial donation treatment at Newcastle, which will be life-changing for them, as they seek to avoid passing on serious genetic diseases to future generations."

Britain became the first country in the world formally to allow mitochondrial replacement therapy (MRT) when the HFEA gave a cautious green light to the procedure last year.

In 2015, MPs and peers paved the way for the change by voting to alter the Human Fertilisation and Embryology Act which sets the legal framework for fertility research and treatment.

Mitochondrial replacement has been made an exception to the general rule which outlaws tampering with "germline" inherited DNA.

A total of 25 patients are now lined up for the first NHS treatments in Newcastle. An initial £8 million has been made available by the NHS to fund the treatments over the next five years.

An estimated one in 200 children are born with defective mitochondrial DNA (mtDNA).

Mary Herbert, Professor of Reproductive Biology at Newcastle Fertility Centre and the University of Newcastle, said her team was "delighted".

She added: "Many years of research have led to the development of pro-nuclear transfer as a treatment to reduce the risk of mothers transmitting disease to their children.

"It's a great testament to the regulatory system here in the UK that research innovation can be applied in treatment to help families affected by these devastating diseases."

Colleague Professor Sir Doug Turnbull, director of the Wellcome Centre for Mitochondrial Research at the University of Newcastle, who has led the way in developing the technique, said: "Mitochondria diseases can be devastating for families affected and this is a momentous day for patients who have tirelessly campaigned for this decision."

MRT is carried out by transferring the genetic material which effectively encodes a baby's identity to a donor egg whose own nuclear DNA has been removed.

Two different techniques may be employed, either before or after fertilisation.

The end result is the same - an embryo containing healthy mitochondria from the donor and nuclear DNA from the baby's mother and father.

Mitochondria only hold around 0.1 per cent of a person's DNA, which is always inherited from the mother. But when mtDNA goes wrong, the results can be catastrophic, leading to a wide range of potentially fatal conditions affecting vital organs, muscles, vision, growth and mental ability.

The new treatments could potentially eliminate the terrible diseases for ever. However, critics see the techniques as the first step down a "slippery slope" leading to "designer" babies and eugenics.

Mark Bhagwandin, from the anti-abortion group Life, said: "We had hoped that the HFEA would have listened to the thousands of people who have expressed concern about three parent embryos. Instead it has ignored the alarm bells and approved a procedure which will alter the human genome.

"Last year the HFEA said it was making a cautious decision to accept applications. There is nothing cautious about the approval of a licence which will result in the uncertain and potentially dangerous genetic modification of human beings."

Professor Adam Balen, chairman of the British Fertility Society (BFS), which represents fertility clinics, said the HFEA's decision marked an "historical step toward eradicating genetic diseases".

Robert Meadowcroft, chief executive of Muscular Dystrophy UK, which has funded MRT at Newcastle, said: "This is wonderful news for the many women we know who have faced heartbreak while trying to start their own family.

"As with many pioneering advances, success can't yet be 100% guaranteed, but today is a happy day for some 2,500 women in the UK who could benefit from mitochondrial donation IVF."