Now he has asked the HFEA for a licence to carry out a controlled trial. But in a sense these are all studies outside of the body, in a test tube. The real study is what happens at the end of the day. We recognise there's an element of risk, but we also recognise that we're not going to get all the answers without attempting a clinical trial. Mixed opinions Medical opinion about spermatids is mixed.
Some scientists believe their use does pose genetic risks.
But the momentum for a formal trial is growing. Among those in favour is one of Britain's best known fertility specialists - Lord Robert Winston, from Hammersmith Hospital in London. There isn't really any serious evidence that you could safely say that injecting a sperm cell, with the right number of chromosomes, is any more risky than injecting a sperm cell. But the HFEA still has reservations. Dr Anne McLaren chairs the authority's working group on new developments in reproductive technology.