From today, lesbian couples who have children through fertility treatment will be able to register both their names on the birth certificate.
The change in the law confers legal parenthood on a biological mother's female partner, and will apply to couples in England and Wales beginning fertility treatment on or after April 6 2009. Prior to this, only the birth mother could be named as a parent.
The Human Fertilisation and Embryology Act was passed by the House of Commons in 2008, granting lesbian couples equal rights as parents.
The Registration of Births and Deaths Regulations have been updated as a result, and from today both women can put their names on the birth certificate of their child born through IVF.
Lesbian couples who are not in a civil partnership will have the same right as unmarried heterosexual couples to sign birth certificates if they attend the local register office at the same time.
Lord Brett, the Home Office minister, said: "This positive change means that, for the first time, female couples who have a child using fertility treatment have the same rights as their heterosexual counterparts to be shown as parents in the birth registration.
“It is vital that we afford equality wherever we can in society, especially as family circumstances continue to change. This is an important step forward in that process."
Critics of the legislation include Conservative MP Nadine Dorries.
"If we want to build a stable society, a mother and father and children works as the best model," she told the BBC. "We should be striving towards repairing and reinforcing marriage. I think this move sends out the exact opposite message."
Labour MP Geraldine Smith agreed: "To have a birth certificate with two mothers and no father is just madness. Common sense has completely gone out of the window.
“It's very unfair on the children for the state to be colluding to hide their real genetic parentage. I think it's putting the interests of adults first, rather than the welfare of the unborn child, and that's contrary to the way the system has always worked in the past."
But Ruth Hunt, Stonewall's head of policy and research, said the change in the law would make life for lesbian couples fairer and easier, and end discrimination.
"As the law improves to provide further equality, knowing your new rights will help people make full use of the services they're entitled to," she said.
"And if discrimination occurs, the same knowledge can help them demand fair treatment. Now lesbian couples in the UK who make a considered decision to start a loving family will finally be afforded equal access to services they help fund as taxpayers."
