Legislation allowing donors to be identified by their genetic offspring would cut off the major source of eggs used in fertility treatment, ending the hopes of women who cannot otherwise conceive a child.

The move, first revealed in The Times on Saturday and confirmed yesterday by Melanie Johnson, the Public Health Minister, would make it virtually impossible for clinics to recruit women to “egg-sharing” schemes, according to experts.

These programmes, by which IVF patients agree to donate some of their eggs in return for discounted treatment, currently provide most of the eggs available to women who produce none of their own.

Even these eggs are already in short supply, with waiting lists of up to eight years.

Paul Serhal, of University College Hospital in London, said that the new rules would make it all but impossible to convince women to participate in egg-sharing schemes, which carry small but appreciable risks to their health.

“I can guarantee that as far as egg-sharing is concerned, you might as well forget about the programme,” he said.

His fears were backed by Kamal Ahuja, of the Cromwell Hospital in London. “If egg donors disappear, as I expect they will, there will be a whole class of infertile women we are going to be forced to turn away,” he said. “The effect will be phenomenal and lasting.”

Donated eggs have always been scarcer than sperm because they must be removed from the body during an invasive operation, which follows a course of drugs to stimulate the woman’s ovaries.

Experts predicted that the prospect of identification would put off many women, who might fail to conceive as a result of their own IVF treatment, and then be confronted 18 years later with biological children brought up by an- other family.

Ms Johnson said that individual women would react to this differently. “In some cases they may be very happy that someone of their genetic stock would want to meet them. In other cases people might find it upsetting.”

More than 1,700 cycles of treatment using donated eggs or embryos were conducted in 2000-01, leading to 465 births. Doctors need to recruit 1,000 new egg donors and 200 new sperm donors annually if they are to keep up with demand.

If egg-sharing ends, women who need donated eggs will usually have to find their own donors, persuading a friend or relative to give eggs for altruistic reasons.

The new measures will remove anonymity from donors who donate after April 1 next year. Children will be allowed to trace their biological parents once they reach 18.

Dr Serhal, however, said this prospect might dissuade many families from telling their children about their origins: the rules will not oblige them to do this. At present, fewer than one in ten children born through donor insemination is told.

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