A company offering to bank frozen embryos in case a sibling might need tissue-matched organs later in life has been denounced by IVF scientists at the American Society for Reproductive Medicine Conference in Washington. The California-based company StemLifeLine claims that embryos can be "transformed" into individual stem cell lines which can create therapies.

However British stem cell experts have called for a reality check. The doyen of British IVF, Lord Robert Winston, said the company was preying on parents' fears. "It's a clear example of exploitation of the worries of couples about the fate of their children. There is no scientific evidence to sustain the notion that this will be a useful procedure. I would be horrified if anyone tried to do this in Britain."

And Professor Stephen Minger, of King's College London said that the idea was profit-driven. "My worry is that this is a commercial service that is being promoted to companies when the science is really not there to justify it. It is like trying to run before you can walk, and the fact it is being done for commercial purposes makes it worse."