Suzi Leather raised a challenging issue for liberals yesterday. The head of Britain's fertility treatment authority suggested that both lesbian couples and single women should be allowed IVF treatment. At the annual meeting of the Human Fertilisation and Embryology Authority, Ms Leather suggested that the current law controlling IVF should be changed so that it no longer took account of "the need of the child for a father".

Ministers have already agreed to review the 1990 law because of the large number of medical and social changes that have occurred in the last 14 years. Currently, for example, there is no requirement for clinics to check whether applicants for treatment are on a paedophile register. But what has caused real ructions is the idea that a child's need for a father could be dropped.

We have no wish to join rightwing commentators, who this morning will be declaring that the new move is further evidence of the decline of civilisation. Indeed, we support the suggestion that lesbian couples should be allowed to have children. There is plenty of evidence showing children thriving in such homes. As Ms Leather notes, "it is the quality of the relationship that matters".

There are also good reasons why single women should have access too. One warm loving parent is better than two cold ones. Tuesday night's programme in the BBC series following 25 children of the new millennium, showed just how successfully even a seriously disabled single mother can bring up a child.

But as Ms Leather noted yesterday: "I think having two parents is better than one, largely on energy grounds." A large number of psychological and sociological studies support this pragmatic approach. Even the director of the National Council for One Parent Families is on record as suggesting: "You would have to be mad to set out to be a single parent." But it is not the effects on the single parent, but on the child that matter. Ms Leather rightly insisted that the welfare of the child should remain a central plank in any new legislation. Against the research evidence, this will be difficult to square that with the right of a single woman having access to IVF.

There are three reasons why ministers may still wish to proceed. First, because parental research is not definitive, and only applies to averages, not individuals. Second, because women can always turn to the unregulated internet where there would be more risk. And third, because some clinics already provide just such a service. We need a debate, but it must be a serious rather than an emotional one.