Doctors at Leicester Royal Infirmary started the investigation after discovering the 20-year-old man was a registered donor at its fertility unit. The man claims to have had sexual intercourse with two women - and given his sperm to eight others for self-insemination.
Since advertisements appeared in the gay press, the donor said he has had 40 inquiries. He said he embarked on the scheme, for which he charges pounds 40 a time, because lesbians were not getting fair treatment from sperm banks.
'I feel that although many people may frown at the thought of lesbian couples having their own children, I know there is a great need for the service that I perform.'
Dr Roger Neuberg, director of the fertility unit, said the matter had been reported to the Human Fertility and Embrology Authority. He said no woman was barred from applying for insemination, but conceded it would be difficult for a single or lesbian woman to be accepted.