So-called "gay marriages" have moved a step closer after plans for legislation were announced in the Queen's Speech.
The law would introduce new obligations for gay couples
The Civil Partnership Bill would enable homosexual "civil partners" to sign a document entitling them to similar legal rights to married couples.
Individuals could also benefit from a dead partner's pension, and a form of divorce could end the agreement.
The proposed law has been welcomed by gay rights groups but is opposed by some Christian organisations.
Deputy Minister for Women and Equality, Jacqui Smith, said last week: "Same-sex couples have been invisible in the eyes of the law for too long.
"The right to be treated equally and fairly is fundamental".
A spokesman for the gay rights group Stonewall said the bill was warmly welcomed.
"We're delighted. This is a hugely significant milestone.
"Hundreds of thousands of gay couples have undergone real suffering because the law does not recognise their long-term relationships."
The moves will allow gay people to benefit from a dead partner's pension and grant next of kin rights in hospitals and exempt them from inheritance tax on a partner's home.
Gay couples would also be able to gain parental responsibility for each other's children and be obliged to support each other financially.
David Allison from the gay rights groups OutRage! also welcomed the bill, but said gay couples' pensions rights should not be postponed until 2010, as is currently specified.
"By and large the government is removing all the overweight legislation that the Tories brought in and are introducing more positive rules that level off gay people and straight people," he added.
Some Christian groups are expected to oppose the introduction of the bill.
Don Horrocks, of the Evangelical Alliance, said it was against the effective creation of gay marriages.
"We are deeply concerned by the proposals.
"Whilst it isn't being called marriage it's the creation of a relationship that is marriage in all but name, all the rights without the commitment.
"It undermines the institution of marriage."
The former Archbishop of Canterbury Dr George Carey recently told the BBC there was nothing "sinister" about same sex relationships or homosexuality.
But he added he did not want to see gay "civil partnership" to be referred to as marriage.