A group of around 500 sperm donors are the biological fathers of more than 6,200 children in the UK.
Each of the men's donations have been used successfully in at least 10 separate cases - and 15 of the men are now biological fathers to 20 or more children, according to figures from the Human Fertilisation and Embryology Authority (HEFA).
Records from fertility clinics across the country show that since 1991 there has been a total of 504 donors who have gone on to be the biological fathers of 10 or more children.
Six of the men have 'fathered' 20 children each from their donations, while another nine donors have 'fathered' 21 or more children.
Many of the children will be raised as siblings, as rules on donation only allow sperm from one donor to be used to inseminate up to ten different families.
Typically, clinics use the sperm from one donor to treat only six women, and nearly 20 per cent of registered donors are never used at all, reports The Times.
The HFEA will not disclose the highest number of children born from a single donor, saying that figure would be in breach of the Data Protection Act.
About 1,000 children are born each year in the UK after conception using donor sperm.
Before 2005, men in the UK who donated their sperm for fertility treatment could remain anonymous and any children born from their donations were entitled to receive only basic physiological details of their biological fathers.
However, in 2005 new laws were put in place that allowed children the right to find out the identity of their biological parents.
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