Babies with two fathers or two mothers could become a reality after a breakthrough by researchers at Cambridge.

They have shown that it is possible to make human egg and sperm cells using skin from two adults of the same sex.

The development could help men and women who have become infertile through disease or gay couples to have children.

But critics voiced concern, arguing that the breakthrough brings closer the prospect of 'designer babies', in which the looks, character and health attributes of children would be selected by parents.

Babies with two fathers or two mothers could become a reality after a breakthrough by researchers at Cambridge (file image)

The scientists from Cambridge University and the Weizmann Institute in Israel used skin from five adults to artificially create 'germ' cells, or stem cells, which make sperm and eggs in the body.

The academics say the cells could also be used as a 'repair kit' to heal tissue in any part of the body.

Jacob Hanna, the specialist leading the project's Israeli arm, said the technique could be used to create a baby just two years from now.

However, he conceded that ethical implications needed to be considered carefully. 'I am not in favour of creating engineered humans ... but I am very confident it will work and will be very relevant to anyone who has lost their fertility through disease.'

The development could help gay couples to have children (stock image)

He added: 'It has already caused interest from gay groups because of the possibility of making egg and sperm cells from parents of the same sex.' The scientists' findings, published in the journal Cell, show that a gene called SOX17 is critical in the process of reprogramming human cells.

Professor Azim Surani, of Cambridge University, told The Sunday Times: 'We have succeeded in the first and most important step of this process, which is to show we can make these very early human stem cells in a dish.

'We have also discovered that one of the things that happens in these germ cells is that epigenetic mutations, the cell mistakes that occur with age, are wiped out. That means the cell is regenerated and reset, so while the rest of the cells in the body have aged and contain genetic mistakes, these ones don't.

'We can't say no mutations are passed on, but mostly it doesn't happen.' The use of manufactured sperm and egg cells would require a change in the law.

Allan Pacey, an infertility expert and professor at Sheffield University, said he was excited by the idea of the technology being used to make sperm for the thousands of men who have been left infertile after childhood cancer.

But David King, director of Human Genetics Alert, a secular organisation critical of the progress in fertility science, said he was concerned that scientists might view the development as a 'convenient route' to creating genetically engineered babies.

It comes as the House of Lords is this week set to approve the use of mitochondrial transfer or 'three-parent baby' technology.

It is designed to prevent devastating diseases caused by faults in mitochondria, which power cells, by swapping them with healthy ones from an egg donor. This will mean children are born with DNA from two women and a man.