In the UK, the law applicable to liability for child maintenance does not restrict it to children conceived in 'normal', conventional, or ongoing relationships. A biological parent has specific legal rights, AND a duty of ‘parental responsibility’ to look after the child.
Mothers automatically have parental responsibility.
A father has parental responsibility if he is married to the child’s
mother, or is named on the birth certificate.
Unmarried fathers do not have automatic parental responsibility, and
neither do step-parents or grandparents.
A proven biological father may not have parental responsibility, but will certainly have financial responsibility. In most cases fathers will have parental responsibility or can easily acquire it by way of an agreement or a court order. Unless there are compelling reasons, the courts are unlikely to refuse it.
If a DNA test shows that the child is yours, then you are liable for the usual contribution to care at CSA rate of 15% of take home pay. When the baby is born the mother can apply to the CSA for maintenance naming you as the father. You will have a limited time within which to ask for (and pay for) a DNA test if you wish to challenge the issue. The cost is repaid if the child is not yours.
Financial liability applies whether or not money has changed hands in return for the sex that led to the child's conception. The issue of casual sex leading to parenthood is a perennial one, and this page is as good as any:
Dating site babies (Leiper Gupta Family Lawyers)
Also in the UK, if you donate sperm through a Human Fertilisation and Embryology Authority (HFEA) licensed clinic, you will not:
- be the legal parent of any child born
- have any legal obligation to any child born
- have any rights over how the child will be brought up
- be asked to support the child financially
- be named on the birth certificate
If you use an unlicensed clinic to donate sperm, or an informal method, you will be the legal father of any child born from your donation under UK law.
Legal rights for egg and sperm donors (UK Government)