British MPs have approved the creation of IVF babies using DNA from three different people in order to prevent inherited diseases.

The historic decision was taken in a free vote after a debate on the controversial issue of mitochondrial donation in the Commons.

It means the UK is now set to be the first country in the world to permit the treatment, which according to critics crosses an unacceptable ethical line.

If the House of Lords ratifies the move - which is likely - the first baby conceived with the procedure could be born by the end of next year.

The child would have "nuclear" DNA determining individual traits such as facial features and personality from its two parents, plus a tiny amount of mitochondrial DNA (mDNA) from an anonymous woman donor.

Research has shown that mitochondrial donation could potentially help almost 2,500 women of reproductive age in the UK.

All are at risk of transmitting harmful DNA mutations in the mitochondria, tiny rod-like power plants in cells, onto their children and future generations.

Mitochondrial DNA (mDNA) is only involved in metabolism and makes up just 0.1% of a person's genetic code. But faults in mDNA can lead to a wide range of devastating and sometimes life-threatening inherited diseases responsible for conditions including blindness, deafness, muscle wasting, diabetes, heart failure and dementia.

The MPs voted through an amendment to the 2008 Human Fertilisation and Embryology Act making mitochondrial donation procedures legal for the first time anywhere in the world.

Supporters of the move argued that it would be immoral not to take advantage of technology that can save families from the misery of serious inherited diseases.

Opponents, including church leaders and pro-life groups, warned that the change was being brought about too hastily and marked the start of a "slippery slope" towards designer babies and eugenics.

Scientists led by Professor Doug Turnbull at the Wellcome Trust Centre for Mitochondrial Research at Newcastle University have pioneered the techniques and hope to be the first group to offer the treatment.

But first their application must be approved by the fertility regulator, the Human Fertilisation and Embryology Authority (HFEA) which has to be satisfied that the procedure is sufficiently safe.

The legal change means the HFEA is now empowered to grant licenses for the treatment, and will carefully consider each application on its merits.

A Wellcome Trust spokesman said: "If its approved by the House of Lords, probably in a couple of weeks, the HFEA and Doug will get together to determine precisely what the application terms should be. We're still awaiting the results of a couple more experiments from Doug's lab.

"Then Doug will apply for the first licence which will be looked at on its individual merits. We might be talking about tens of families that could be eligible for the treatment. What will happen is that each application will be made on a case-by-case basis.

"Once we have the licence then we can go ahead. Our estimate is that the first licence will be applied for in November this year, and the first baby might be born in 2016."

She said that despite the enormous amount of publicity expected, the scientists intend to put the interests of the family and research needs first.

"Even if it's the sort of family that's comfortable with publicity, Doug is being very cautious because of the extra pressure from having lots of cameras around, for instance," she added. "He wants to be sure that the science is absolutely as good as it can be."

With the family's permission, the team planned to monitor the newborn child closely for some years in case of any hint of abnormality.

The eyes of the world were on the MPs as they discussed the arguments for and against mitochondrial donation and filed through the division lobbies.

Before the vote, international charities and campaigners wrote an open letter to the politicians urging them to back the change in the law.

Signatories included groups from the US, France, Germany, Spain and Australia. In their letter, they described mitochondrial diseases as being "unimaginably cruel" and inflicting pain "that cannot be imagined".

Until now, any tampering with "germline" DNA - genetic material in sperm and eggs that is inherited - has been unlawful. That included mitochondrial DNA, which is only inherited from a child's mother.

When the Human Fertilisation and Embryology Act was updated in 2008 legislators deliberately left a door open for the future possibility of preventing mitochondrial disease.

But to become law, it required Parliament to approve the introduction of new regulations.

Two mitochondrial donation techniques have been developed, both of which involve transplanting a mother's nuclear DNA into a de-nucleated donor cell.

The mother's nuclear DNA then sits in a cell whose body material - the cytoplasm - contains healthy mitochondria. From then on, those mitochondria, and their healthy DNA, can be transmitted to future generations, thereby breaking the chain of inherited disease.

The chief difference between the two techniques is that one is carried out before fertilisation and the other after.

An HFEA spokesperson said: "If both houses of Parliament pass the regulations, our task will be to design a process for considering licence applications to carry out mitochondrial donation in a clinic.

"We have many years' experience of rigorously licensing procedures of this kind, such as PGD (Pre-implantation Genetic Diagnosis), and will design a process which considers both the latest scientific advice and the individual facts of each case when reaching a decision."

Former HFEA Chair Professor Lisa Jardine, who led the consultation process on mitochondrial replacement between 2011 and 2014, said: "This is just the beginning of a lengthy process. No-one is suggesting that there are no scientific issues still to be resolved. At every stage, the scientific review body has stressed that more experiments will need to be carried out.

"However it is perfectly reasonable that after a three-year public debate the time is ripe for this technique to be made lawful, allowing the full regulatory process to begin."

Dr Jeremy Farrar, director of the Wellcome Trust, said after the vote result was announced: "Families who know what it is like to care for a child with a devastating disease are best placed to decide whether mitochondrial donation is the right option for them.

"We welcome this vote to give them that choice, and we hope that the House of Lords reaches a similar conclusion so that this procedure can be licensed under the UK's internationally-admired regulatory system.

"This is a vote of confidence in the patients, scientists, doctors and ethicists who have worked hard for a decade to explain this complex research to politicians, the public and the media, and in the exemplary process for reviewing scientific, ethical and public opinion led by the Human Fertilisation and Embryology Authority."

Robert Meadowcroft, chief executive of the Muscular Dystrophy Campaign, which supports families affected by mitochondrial disease, said: " We have finally reached a milestone in giving women an invaluable choice, the choice to become a mother without fear of passing on a lifetime under the shadow of mitochondrial disease to their child. Today, MPs have responded to the broad public support for mitochondrial donation IVF, which follows years of ethical, scientific and public consultations.

"There are currently no means to treat devastating mitochondrial diseases, which can cause muscle wastage, loss of vision, stroke-like episodes and a premature death. Preventing inheritance, where possible, remains our only option, and that is why we have invested in and wholly support this pioneering technique.

"The next step is for us to make sure peers are armed with the full facts surrounding mitochondrial donation IVF ahead of a debate in the House of Lords. It is absolutely crucial that they fully understand what is at stake for women affected by this condition."