The Human Fertilization and Embryology Authority approved the research. Kathy Niakan, a stem cell scientist at the Francis Crick Institute, and her colleagues plan to use the technique to study the genes involved in how embryos develop, not as a treatment for genetic diseases.

But some worry the work could lead to "designer" babies whose DNA has been carefully chosen to have desirable traits.

"This is the first step on a path that scientists have carefully mapped out towards the legalization of [genetically modified] babies," David King, of anti-gene manipulation group Human Genetics Alert, said at a meeting last month, AP reports.