MPs will consider measures that ensure equality for lesbians when accessing fertility treatments this afternoon.
The Human Fertilisation and Embryology Bill also allows for the creation of animal-human embryos for research purposes.
Roman Catholic MPs are expected to challenge the removal of a requirement for doctors to “consider the need for a father” when deciding to consent to IVF or assisted conception treatments during .
The bill proposes to replace that with a need for “supportive parenting.”
Many lesbians are refused treatment by doctors under the present arrangements.
The decision to grant Labour MPs a free vote at next week’s committee stage was controversial as the Prime Minister appeared to be bowing to pressure from religious groups.
Lib Dem and Tory MPs have a free vote at all stages of the bill.
As many as 12 ministers, three of them in the Cabinet, were reported to be considering leaving the government rather than vote for parts of the bill.
The Cabinet ministers thought to object are Ruth Kelly, Transport Secretary, Defence Secretary Des Browne and Paul Murphy, the Secretary of State for Wales.
At Easter the leader of Scotland’s Roman Catholics, Cardinal Keith O’Brien, claimed that the Human Fertilisation and Embryology Bill will create “Frankenstein-like” human-animal hybrid embryos, a charge rejected by the government and scientists.
He accused Prime Minister Gordon Brown of: “promoting a bill which denies that a child has a biological father, allows tampering with birth certificates, removing biological parents, and inserting someone altogether different.”
The Cardinal also accused the government of trying to challenge “standards by which we have lived throughout our lives and by which Christians have lived for the past 2,000 years” and of not responding to the church’s concerns.
In November 2006 Cardinal O’Brien compared same-sex partnerships to paedophilia and also spoke against gay adoption.
The government’s position remains that given the legal recognition of civil partnerships and laws preventing discrimination on the grounds of gender and sexual orientation, retaining any provision that mentioned a mother and a father is inconsistent with the wider government policy of promoting equality.
In March the Prime Minister’s spokesman called the bill “an important piece of Government business; it was in the Queen’s Speech and it was the Prime Minister’s view that it was important that the bill as a whole was passed.”
He pointed out that all Labour MPs would be expected to support the bill as a whole during today’s second reading and its later stages.
“We had always said that this would be treated as government business but we would find a mechanism by which individual MP’s could express their conscience and that was what we were doing,” he said.
Labour MPs will be allowed a free vote on two other clauses in the Human Fertilisation and Embryology Bill during next week’s committee stage.
One allows the creation of human-animal embryos for medical research and the other the creation of so-called “savour siblings,” who would aid a sick brother or sister.
More than 200 charities have written a joint letter to all MPs.
“The bill will allow new avenues of scientific inquiry to be pursued which could greatly increase our understanding of serious medical conditions affecting millions of people throughout the UK,” they said.
The respected peer and fertility expert Lord Winston accused the Roman Catholic church of “misleading” the public about the nature of the science involved.
“I’m afraid that when the Church, for good motives, tells untruths, it brings discredit upon itself,” he said.
Tory leader David Cameron said in March:
“My own view, and I think [that of] many people in the Conservative Party, is we need to update the legislation.
“This sort of research is important. We all want to see diseases reduced and problems that children have, birth defects, dealt with.”
The Observer reports that MPs plan to table an amendment today reinstating the “need for a father” provision.