Plans to allow unmarried heterosexual and gay couples to adopt children could be blocked by peers.

What we need to do very urgently is widen the poll of prospective adoptive couples

Lord Clement-Jones Lib Dem peer

Family values campaigner Lady O'Cathain will lead the challenge in the House of Lords on Wednesday, after MPs voted earlier this year to scrap the ban.

The Conservative peer claims backbench MPs have been "got at by the gay rights lobby", but supporters of the plans say too many children are still waiting to be adopted.

She claims cross-party support for her stance in the Lords, although the government could try to overturn it in the House of Commons at a later date.

Marriage

Gay rights campaigners claim opponents of change are putting their objections to homosexuality before the interests of children.

In the event of my death I do not want my children to be adopted by homosexuals

Christian Institute "adoption card"

Lady O'Cathain claims the proposals will undermine marriage and put children at risk by placing them in unstable relationships.

She argues "political correctness" among the authorities means many married couples who want to adopt are being turned down for reasons such as "being too rich, too fat or their house is too big".

Cohabiting couples who make a commitment to look after a child should also make a commitment to each other and get married, she adds.

"I'm not gay bashing. I am pro-children. But they are so vulnerable and don't have a voice.

"The children in care are damaged and need stability. My gay friends all tell me they agree with what I am doing."

Lady O'Cathain was asked to take up the fight against same sex adoption by ex-leader of the Lords and family values campaigner Baroness Young, before her death from cancer last month.

MPs 'got at'

Campaigners argue the proposals were not included in the government's original White Paper on adoption, published in 2000, but were added later by a backbench amendment.

"And I'm afraid the gay rights lobby got at the backbenchers," Lady O' Cathain claimed.

Iain Duncan Smith says children's welfare is the key issue

The Tory peer is backed by pressure group, The Christian Institute, which this week launched a new "adoption card" for parents who oppose gay adoption.

It carries the declaration: "In the event of my death I do not want my children to be adopted by homosexuals."

An ICM poll commissioned by the Christian Institute, suggested that more than 70% of parents in the Prime Minister Tony Blair's Sedgefield constituency appeared to oppose plans to allow gay men to jointly adopt children.

But a MORI poll for the British Association for Adoption & Fostering, suggested 44% of adults in the UK believe the law should be changed so that gay and lesbian couples in stable and long-term relationships should be allowed to adopt a child together.

Under current law, only married couples and single people, including gay people, are allowed to adopt.

They should be allowed to adopt

Kirstin Lynch, Greece

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Compromise?

Lady O'Cathain said changes to adoption law had already meant more and more children were being adopted.

That point was disputed by Liberal Democrat peer Lord Clement-Jones, who said 5,000 children were still awaiting for families to adopt them.

"What we need to do very urgently is widen the pool of prospective adoptive couples," he told BBC Radio 4's Today programme.

Unmarried couples were more likely to want to adopt, he argued, and there were strong tests to ensure children got loving families.

Peers may decide to back an alternative, less hardline proposal when they debate the Adoption and Children Bill on Wednesday evening.

Homophobia denied

This would extend adoption rights to heterosexual cohabiting couples, but not to gay partners.

Peers will be given a free vote on the issue, but Tory members will be under a whip to attend.

Conservative leader Iain Duncan Smith has insisted his party's opposition to lifting the ban on adoption by gay and unmarried couples was not down to homophobia but centred on children's welfare.

Mr Duncan Smith has said he believes it is wrong for unmarried couples to adopt because statistics showed they were more likely to split up than those who had wed.