Her carpenter father had been an insulin-dependent diabetic who died when she was six. Christine and her mother never got on.

　　 Ten years ago, Christine's mother referred to the secret directly for the first time.

　　 "She told me that I had been conceived through donor insemination (DI) at the Margaret Jackson clinic in Exeter," says Christine. "I was 40 when I found out that my father was a glass jar with a blob of sperm in it. My father doesn't have a face, or a name and he wasn't even a one－night stand. If my mum had had an affair at least there would have been sex and lust, something human rather than something so cold, scientific and clinical. My parents never even met. How weird is that? I still feel like a freak, a fake. I don't feel I know who I am any more."

　　 Between 1940 and 1983, 483 children were conceived through anonymous DI at the private Exeter clinic, most by affluent middle-class mothers, not factory girls like Christine's mum. Christine has never knowingly met a single one of them, though it's almost certain that some-even scores - are her half - siblings. She has no way of tracking the donor or her half-siblings down. Christine has no access to records, and it is likely that none survive. She has no rights to know anything about the man who helped give her life. The situation hurts. 'I was only made to assuage my parents' reproductive vanity,' she says bitterly.

　　 Almost 18,000 babies have been born through donated gametes (sperm and eggs) and embryos in the UK since the regulatory Human Fertilisation and Embryology Authority was set up in 1991. Anonymous donations have allowed infertile heterosexual couples, gay couples and single women to create families that would otherwise never have existed. Between 1940 and 1990, tens of thousands more were conceived mainly using donated sperm, the low-tech end of gamete donation which has been around for over a century.

　　 While the first baby conceived with a donated egg was not born until 1987, the first documented case of donor insemination took place in 1884, when the Philadelphia-based doctor William Pan coast inseminated a sedated woman with a medical student's sperm without her permission or knowledge. Sperm insemination remains, by far, the most common donor conception procedure.

　　 No one can say exactly how many people alive in Britain today were conceived through donor conception-estimates put it at around 40,000.

　　 The received wisdom was that secrecy was in everyone's interests. The biological mother and her husband usually wanted to pretend that, genetically, the child was completely theirs. The clinics encouraged women to go home after artificial insemination and make love with their infertile husbands. Then the couple could cling to the possibility-however remote-that the child was really theirs. Some clinics even mixed a sterile husband's sperm with the donor's to keep the parental fantasy alive.

　　 The donor dads were shadowy figures, guaranteed anonymity by the clinics. That way there was no risk of the past -- and, conceivably, hundreds of offspring -- returning to haunt the donors, and clinics did not have the expense and hassle of records. Keep it secret, it's simpler, advised the doctors. But it is not proving that easy. Someone forgot that gurgling, happy babies grow up into adults with complex needs.