Every year in the UK, thriving babies are born from frozen embryos. The success rate may be modest - there were 3,002 embryo transfers in 1993, a clinical pregnancy rate of 15.9 per cent, and a live birth rate of 12.7 per cent - but to childless couples the arithmetic is not insignificant.

Freezing embryos allows patients to plan their infertility treatments and their families, to avoid repeating miserable drug regimes to boost fertility, and to have fewer embryos replaced on each occasion, reducing the risk of multiple pregnancy.

There could be many reasons why couples lose touch with their clinics, according to Jennifer Woodside of the Human Fertilisation and Embryology Authority, although the clinics do try to contact them every year. Since the impending disposal of embryos was reported, more contacts have been made, and couples have been coming forward. Some people undoubtedly cannot face making a decision, so make it by default. Others may have been divorced, or moved abroad.

Some couples are resistant to donating an embryo. "Sometimes women are more willing to donate an egg than an embryo," says Ms Woodside. "Many do have problems giving an embryo to someone else. But they may not want it to perish, and many prefer that their embryos be used respectfully in research projects, perhaps to help others with fertility problems."

Embryo research is permitted for five purposes:

To promote advances in infertility treatment;

To increase knowledge of congenital diseases;

To increase knowledge of the causes of miscarriage;

To develop more effective techniques of contraception;

To develop methods for detecting gene or chromosomal abnormalities in embryos before implantation.