The Human Fertility and Embryology Authority (HFEA), the UK's fertility regulator, has admitted breaches of the sperm donation limit have occurred, following news that one donor has fathered 17 families.

According to current regulations, one donor's sperm may be used to create up to ten families. This rule is in place in order to limit the risk of offspring meeting and having an incestuous relationship. In addition to the donor who has fathered 17 families, another donor has created 12, and three more donors have all fathered 11 families.

Alan Doran, chief executive of the HFEA, will be issuing written warnings to fertility clinics in the UK after it emerged that the exact number of breaches is unknown. If there are any further violations the clinic in question may lose its licence.

'There is a real danger in a small country like the UK for donor-conceived children to meet up unknowingly with half-siblings', said Josephine Quintavalle, of the campaign group Comment on Reproductive Ethics. 'It is truly lamentable that the HFEA has such inadequate systems in place that it is unable to monitor properly the numbers of babies conceived in this way'.

The ten-family limit was imposed not only to make incestuous relationships less likely, but also to limit the number of half-brothers and -sisters a child from a sperm donor may have.

As there are no limits on how many children recipients can have using donated sperm, it is unknown how many children this donor may have. According to the Office for National Statistics, the average British family has 1.9 children, which suggests the man who has fathered 17 families may have 34 children.