The Liberal Democrat conference meeting this week in Liverpool has overwhelmingly backed a resolution calling for marriage equality, irrespective of sexual or gender orientation.
Party activists made it clear they also want same-sex couples to be free to have a church wedding, as well as for heterosexual couples to be able to have civil partnerships.
But they also made it clear that there was no intention to force church or other faith communities to offer ceremonies to people.
The resolution was supported by a string of MPs and delegates, including former Met police assistant commissioner Brian Paddick, a Christian, who married his partner in Norway last year.
He declared: “We are married. It is important. Yet we are only married in Norway. Here it reverts to a civil partnership and that doesn't feel the same at all.
“Yes, we have to be sensitive to religions and what they feel on this issue, and we are not talking about forcing religions to marry same-sex people in their synagogues and churches and temples. But there should be equality. If I want to marry my same-sex partner then I should be allowed to do that.”
MP Stephen Gilbert said: "Let's be clear. This motion doesn't compel religious groups to offer gay marriage or compel gay people to get married. It simply extends an equal choice to one and all.”
Delegates at the party's annual conference in Liverpool support call for marriage equality for lesbian, gay, bisexual and transgendered people
Evan Harris, the former MP for Oxford West and Abingdon, said the motion would "test" the Conservatives' commitment to equality and would strengthen the hand of Lib Dem equalities minister, Lynne Featherstone, in pressing for a change in the law.
Harris told delegates at the party's annual conference in Liverpool that the party should use the fact that it was part of the coalition government to "seize the moment to push the agenda forward on full equality".
Harris challenged the belief that equality for lesbian, gay, bisexual and transgendered people (LGBT) had been achieved under the Labour government following a raft of legislation over the past 13 years, including lowering the age of consent and introducing civil partnerships for same-sex couples.
Section 28, the legislation introduced under the Conservatives that banned the "promotion of homosexuality" by local authorities, took many years to repeal, he said, and Labour also held back from outlawing gay discrimination in the armed forces until a court ruling overturned the decision.
Hailing the Lib Dems' record on equality issues, Harris said: "We have never failed to do that in the past. There's plenty of work still to do. Let's give Lynne and other Liberal Democrats in government something to get their teeth into."
A change in the law would ensure transgender people would not be forced to divorce their wife or husband before they could achieve a gender change, he went on.
Aware of the sensitivities of religious groups, he insisted the motion would not force religious groups to conduct ceremonies if they did not wish to do so.
Liz Williams, an Anglican from the Leyton and Wanstead branch and a member of the party's Christian fellowship, told delegates that she has supported same-sex marriage for 20 years because her faith taught her that marriage was a sacrament and an outward, physical sign of an inward and spiritual grace.
She declared: "The grace of marriage is the love that unites people. I cannot deny and do not want to deny in the lives my gay, lesbian, transgendered and bisexual friends, the same love and grace that I espouse and display in my own."
Supporters of the change argue that civil partnerships, which were introduced in Britain five years ago, fall short of marriage, and that it is unfair that gay couples are barred from a full religious ceremony.
But the resolution may prove a sticking point for the coalition government because parity of treatment will be strongly opposed by socially conservative Tories, both religious and non-religious.
Deputy PM Nick Clegg, a Lib Dem, and Conservative PM David Cameron are understood to be in talks about the issue.