Five hundred sperm donors in the UK have been confirmed to have fathered over 6,200 children between them – an average of 12.4 children per man. Fifteen of these men are now the fathers to 20 or more children each.

The Daily Telegraph reports that records released by the UK’s Human Fertilisation and Embryology Authority (HFEA), which cover donor insemination figures from clinics across Britain, have identified the “top 500” donors.

Donor-conceived people frequently seek out their natural parents and half-siblings and websites and organisations have been established to facilitate this.

Before 2005, men who sold their sperm for fertility treatment were guaranteed anonymity, and their offspring only had access to basic physiological and medical details about their fathers. But a change in the law gave children the right to find out the identity of their biological parents upon turning 18. However, this is dependent upon the child being told that they were conceived using third party eggs or sperm.

The HFEA will not disclose the most children born from a single donor, saying that figure would be a breach of the Data Protection Act. But the new figures do show there are a total of 504 donors who have gone on to be the biological fathers of ten or more children. Of those, six have 20 children each from their donations while another nine have 21 or more children.

UK rules on sperm donation allow sperm from one donor to be used in 10 different families, meaning that some of the donors will have created extended families of half-brothers and half-sisters. This raises serious ethical issues, particularly if the the half-siblings do not find out that they are related.