The government will try to overturn a defeat in the House of Lords which would prevent gay and unmarried heterosexual couples adopting children.

Peers narrowly rejected the plans already agreed by MPs to end the present system where only married couples and single people can adopt.

What I cannot agree with is that a child in institutional care is better off than in a loving, caring home

Lord Alli

They voted by 196 votes to 162 to maintain the ban on unmarried couples, including gay partners.

The Adoption and Children Bill will now return to the Commons but faces a tight timetable.

MPs are almost certain to overturn the defeat but ministers want to get the laws on the statute books before this session of Parliament ends in less than a month's time.

Marriage

Social Services Minister Jacqui Smith said she was disappointed by the vote.

"Given the strong views of the House of Commons on this issue the Government intends to allow another free vote once the bill returns to the House of Commons," said Ms Smith.

Supporters of the proposals say too many children are still waiting to be adopted.

But Conservative Baroness O'Cathain, who has led the campaign to retain the ban, said the proposals would undermine marriage and put children at risk by placing them in unstable relationships.

Lady O'Cathain said she was urged to take up the fight by fellow Tory peer Baroness Young just 12 hours before she died last month.

Large turnout

Peers were given a free vote on the issue at the end of a highly-charged three hour debate.

Twenty Labour peers backed the Tory amendment blocking gay and unmarried adoption, as did 48 crossbenchers and two bishops.

Among those on Labour's benches who supported the move were Lord Ahmed and Baroness Uddin.

The Bishop of Chelmsford, the Rt Rev John Perry and the Bishop of Winchester also voted to restrict adoption to married couples.

Stability

Tory health spokesman, Earl Howe told peers: "Perhaps the thing I object to most, if this bill were to go through now as it is, is that for the purposes of adoption the law would place marriage, co-habitation and gay partnerships on a platform of legal equivalence.

"The fact of a couple being married would carry no weight at all in any choice between alternative sets of adopters."

Lord Howe said marriage provided the best chance of stability for children who had already suffered turbulence in their lives.

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

Personal blow

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

Wednesday's vote will come as a particular blow to Lord Alli.

The Labour peer, who is gay, gave a personal commitment to become an adoptive parent with his long term partner if the law was changed.

Lord Alli said the current debate had "set married couples against unmarried couples and married couples against gay couples" when what was needed was to find homes for children in institutional care.

Lord Alli said he would "happily agree" that married couples should have priority over both gay and unmarried couples.

But he added: "What I cannot agree with is that a child in institutional care is better off than in a loving, caring home."