Many parents who chose not to tell were concerned, she said, that they would be able to give relatively little information about the biological parent - as sperm donation is carried out on an anonymous basis.

BBC: Donor sperm children 'kept in dark'

But the true extent of the problem is largely unknown because there are no official figures on waiting lists for sperm and egg donation around the country or data on the number of British patients travelling abroad for treatment.

BBC: Home pregnancy test (AJ photo/Science Photo Library)

The body that regulates IVF clinics in the UK, the Human Fertilisation Embryo Authority (HFEA), concedes that provision is "patchy" in parts of the country but says both sperm and egg donation was falling long before the change in the law.

BBC: Home pregnancy test (AJ photo/Science Photo Library)