The government's decision to remove anonymity from sperm and egg donors could halve the number of people willing to donate and make infertile couples turn to friends and family for donations, according to new research.

The change in the law, which took effect in April, means children born from donated sperm or eggs can request details of their genetic parent when they reach 18. Ministers had reassured fertility clinics that overall numbers of donors were unlikely to fall. But speaking at the American Society for Reproductive Medicine in Montreal, Professor Eric Blyth, of Huddersfield University, said analysis of a Department of Health survey of 133 sperm and egg donors showed only half would continue to donate if they lost their right to anonymity. "Their concerns ranged from worries about financial responsibility, their emotional response and fears of personal involvement," he said.

A further study by the researchers, in which counsellors in fertility clinics were interviewed about the impact of the change in the law, found that infertile couples might react by asking close friends or family members to act as donors.

Professor Ian Craft, director of the private London Fertility Centre, said: "In Britain donors have dried up ... and we are seeing more reproductive tourism."