In a letter to all fertility centres, sent this week, Ruth Deech, who chairs the authority, has told clinics it does not ethically approve of the scheme. "It has now come to the HFEA's attention that some centres have presented the decision to allow the practice of egg sharing to continue as giving ethical approval to such arrangements. This is not the case," she wrote.
"While the authority was persuaded that, if properly regulated and monitored, the practice could in some cases be beneficial to participants, it did not give ethical approval to such arrangements.
"As a result, the HFEA must ask all centres to remove any statements suggesting its approval of egg-sharing arrangements from their patient literature and advertisements."
The egg-sharing scheme involves a woman, whose only means of becoming pregnant is to have in-vitro fertilisation, agreeing to donate half her eggs to another woman who cannot produce eggs. In return, the donor pays nothing or reduced rates for her treatment.
Last year the HFEA almost banned the system after a patient trying for a baby was heartbroken to learn that another women had been successful using one of her donated eggs.
The HFEA feared that donors might be "financially induced to do something they would not otherwise do, and which they may regret later on in life".
The authority backed down after protests from some fertility experts who said egg sharing helped women who could not afford IVF treatment and removed the health risks associated with the alternative, in which healthy volunteers supply eggs.
Clinics such as the Cromwell Hospital in London have recently placed advertisements for egg-sharing schemes, which say the practice was "approved by the HFEA in December 1998". Dr Kamal Ahuja, director of the IVF centre at the Cromwell, which is the biggest egg-sharing centre in Britain, described the authority's letter as "very strange".
"We thought egg sharing had been approved last year. They seem to be saying they approve it but it is not ethical ... We await their guidelines and remain convinced that egg sharing is the way forward."
However, Professor Ian Craft, of the London Gynaecology and Fertility Centre, said the recent promotions for egg-sharing schemes gave unreal expectations to donors and recipients. "It can mesmerise participants into believing they are doing good whilst actually reducing their overall chance of succeeding with their own eggs," he said.
The authority is consulting the British Fertility Society and the Royal College of Obstetrics and Gynaecology, and expects to issue interim guidelines by the end of the year.