An embryo belonging to a couple being treated at a Cardiff fertility clinic was accidentally implanted into the wrong woman and subsequently destroyed. The prospects of Deborah, who is 40, having another child with her partner Paul, 38, are slim and both are said to be devastated that their last hope of conceiving a sibling for their six-year-old son has been lost.

'In less than 10 seconds our wonderful world was shattered when the senior embryologist stood in front of us and said, 'I'm very sorry to tell you, but there's been an accident in the lab. Your embryo has been destroyed', the woman told the Mail on Sunday newspaper. It was only after the incident that the hospital came clean with the couple and told them that their embryo had in fact been implanted in the wrong woman and then any potential pregnancy terminated using the morning after pill.

The couple have recently succeeded in claiming damages against the University Hospital of Wales, where the incident took place in December 2007. If the other woman's pregnancy had been allowed to go ahead, it would have meant a further court case to decide who would have custody of the child, according to the couple's lawyer, Guy Forster of Irwin Mitchell.

Ian Lane, Medical Director of the Cardiff Vale NHS Trust which governs the University Hospital of Wales, has apologised 'unreservedly' for the mistake. 'This was a rare but extremely upsetting incident for everyone involved and we take full responsibility for the distress caused to both couples and their families,' he said.

The IVF mix-up happened when a trainee embryologist took the embryo from the wrong shelf of the incubator. Forster called the incident 'an accident waiting to happen' and said that the hospital had been involved in two 'near misses' during the year prior to the incident and that the Human Fertilisation and Embryology Authority (HFEA) had previously warned the hospital to ensure basic operating procedures were carried out, particularly following some similar cases in recent years and an official enquiry into how such mistakes could have happened.

Speaking to the Times newspaper today, Gedis Grudzinskas, a consultant in infertility and gynaecology, said that samples in all hospitals should be electronically tagged to avoid further mix-ups. 'The technology for tagging will minimise the risk and increase confidence in fertility treatment, because this case in Wales shows that things are still going wrong,' he said, adding that the standard measures set in place by the HFEA to prevent further IVF mix-ups, such as 'double witnessing' had clearly proved insufficient.