According to the Human Fertilisation and Embryology Authority:

Mistakes and near misses in fertility treatment are recorded by the Human Fertilisation and Embryology Authority but until now details of the most serious cases have been kept secret.

Last year there were 182 incidents out of 52,000 cycles of treatment provided in Britain, the HFEA said.

Eight of these were given grade A status, meaning they were the most serious incidents could involve events such as embryo mix ups, the death of a patient or an incident which affects a number of patients, for example, when a storage unit malfunctions and all embryos are defrosted and lost.

In 2007/8 two of the eight grade A incidents involved mix-ups. A spokesman refused to give details but said they could be cases where the wrong sperm was used to fertilise and embryo or the wrong embryo was defrosted for use, but neither involved the implantation of wrong embryos.