A child may only have two legal parents – although this is contradicted, for example, by Re G (Children)  UKHL 43 in which the child seems to have had three mothers.
Under legislation introduced in April 2009 the legal mother continues to be the woman who carried the child, regardless of how the embryo came to be in her womb, and regardless of genetics. She ceases to be the mother if an Adoption Order or Parental Order is made.
If a female partner, whether joined by a civil partnership or not, is considered to be the child’s other parent, no man can also be considered the child’s parent, even if biologically he is the father. Such a man would therefore not have the automatic right to apply for a Contact or Residence Order and would need the leave of the court. Such a child would legally be fatherless, which contradicts the view confirmed by the courts that he has the right to know his biological identity; see Mikulic v Croatia  1 FCR 720 and R (Rose and another) v Secretary of State for Health and another  EWHC 1593;  3 FCR 731.
There are anomalies in this brave new world: where two gay men care for a child they are to be regarded as the ‘parents’ but not as the ‘fathers’. Consider a situation such as surrogacy in which a child can have a biological mother (who provides the egg), a mother who carries and gives birth to the child, and an adoptive mother. Consider, also, a case in which a wife leads her husband to believe that he is the biological father of her boyfriend’s child, and where she then divorces her husband and marries a third man. All three men will have a relationship with the child, and may have a legitimate claim to contact, but cannot be regarded as ‘parents’ since a child can only have two.
The legal definition of a parent establishes at once a further discrimination under the law between the sexes; legal motherhood is based on whether the woman in question carried the child, regardless of genetics. Legal fatherhood, on the other hand, is based on genetics.
A man will also be presumed to be the father if:
· He was married to the mother at the time of birth (if he was unmarried at the time of conception the rule still applies) – this rule is known as pater est quem nuptiae demonstrant or pater est for short;
· His name is on the birth certificate;
· He has a Parental Responsibility Order by consent (the CSA will accept this though the courts may not); or
· There are other corroborative factors – e.g. he slept with the mother on the night of conception.
Legal changes introduced under the Human Fertilisation and Embryology Act 2008 complicate matters further by establishing a third category of legal parent who is neither the father nor the mother of the child, but the ‘other parent’; similarly, someone who is either the father or the mother may not necessarily be the legal parent. These changes will affect adoption as well.
The notion of fatherhood has become fragmented, and commonly must be shared between two or more men: the genetic father, the mother’s husband, mother’s ex-husband, mother’s boyfriend, etc. This is particularly so in cases of Assisted Reproductive Technology or ART. The new legislation effectively eradicates the concept of fatherhood and introduces the term ‘other parent’ who can be either male or female.
· If the mother is married at the time of impregnation her husband is regarded as the child’s father regardless of whether or not the sperm is his. If the sperm is not his and he did not give his consent to impregnation, he is not to be regarded as the father.
· If the mother is not married and there is no other adult regarded as the ‘other parent’ and the impregnation was carried out by a licensed provider and the ‘agreed fatherhood conditions’ were satisfied, that man is regarded as the father.
· The agreed fatherhood conditions are:
Ø that the man has given his consent to be regarded as the father under licensed impregnation;
Ø the mother has given her consent that the man be so regarded;
Ø neither has withdrawn their consent;
Ø the mother has not given her consent that another adult be regarded as the parent of the child; and
Ø the mother and father are not in a prohibited relationship to each other.
· A sperm donor is not regarded as the father of a child if he donates through a licensed provider. If he donates on a do-it-yourself basis he will be regarded as the father and will be liable for child support if nothing else; see Re M (Sperm Donor: Father)  Fam Law 94. If the man dies after donation he is not regarded as the father.
· If the mother is in a civil partnership with another woman at the time of impregnation, the other woman is regarded as the ‘other parent’, she has Parental Responsibility and the child is legitimate. If the other woman did not give her consent to impregnation she is not to be regarded as the other parent.
· If the mother was not in a civil partnership with another woman and no other adult is regarded under the above rules as the other parent of the child, but the mother is in an informal relationship with another woman and impregnation is carried out by a licensed provider then the other woman is to be regarded as the other parent. If the two women are joined in a civil partnership before the birth of the child, the child is legitimate.
 See inter alia Fragmenting Fatherhood by Richard Collier and Sally Sheldon, 2008