Lesbian couples who have children together through IVF treatment must be aware that they do not have automatic parental rights if they split up, a legal expert has warned.

The Human Fertilisation and Embryology Act 2008, which came into force last month, means that lesbian couples who are not in a civil partnership can share equal responsibility for a child born as a result of IVF rather than the birth-mother only.

The right is automatic for those in civil partnerships.

However, couples must register their agreement to become joint parents in writing in a prescribed form to ensure they have legal protection if they separate.

Family lawyer Peter Morris, a partner at Irwin Mitchell, said: “In a same sex relationship, only the parent related by birth automatically has parental responsibility for a child which gives them the legal status to take decisions affecting the child. This includes decisions about the child’s name, their medical treatment, schooling arrangements or religious upbringing.

“In the past it has been known for fertilisation clinics to mistakenly tell couples that they will both have parental responsibility so this new Act is a welcome step.”

Morris added he had seen cases which showed the new law was necessary, including one where a client and her partner had split due to the pressures of starting a family. The couple had cared for the child equally but the client was then excluded.

He said: “The only way we were able to acquire parental responsibility was by applying for a ‘residence order’ setting out how they would jointly share the care of their child and parental responsibility automatically follows for both parents by law. Although we were successful, this was extremely costly and traumatic.”

He added: “It is good that a widely misunderstood area of law has been addressed but I think it would be clearer if parental responsibility was the norm for couples undergoing IVF treatment, not the exception. In the long run it would be far more damaging for both the couple and the child involved if there is an on-going dispute over co-parenting and parental responsibility – automatic rights would help to prevent that.”

The law is set to be expanded in April 2010, when male couples will also be able to apply for a Parental Order to be recognised as the parents of children born through surrogacy.