Gay lobbying charity Stonewall says it will campaign for lesbian and gay couples to have civil marriages in the UK.

The charity has come under pressure in recent months from several of its co-founders and other gay campaigners to widen its remit on the issue.

In a statement posted on its website, the group said: “Stonewall is pleased to be widening its campaigning objectives to include extending the legal form of marriage to gay people.

“We seek to secure marriage for gay people as a civil vehicle on the same basis as heterosexual marriage, available in a registry office but without a mandate on religious organisations to celebrate it.

“We seek to retain civil partnerships for lesbian and gay people recognising their special and unique status.”

A spokesman confirmed that the charity will not be lobbying for civil partnerships to be opened up to straight couples.

He said: “We don’t have a view on whether heterosexuals should be entitled to enter civil partnerships. Our charitable remit is to advance human rights for lesbian, gay and bisexual people. Others of course are free to pursue such a change.”

In September, Stonewall said: “Campaigning to end heterosexual disadvantage is not one of [our] charitable objectives.”

A recent PinkNews.co.uk poll of 800 readers found that 98 per cent wanted the right to marry. Seventy-seven per cent agreed that marriage and civil partnerships should be open to everyone, while 23 per cent said that marriage should be the only form of recognition for all couples.

Gay rights activist Peter Tatchell, who is organising a legal challenge against the UK’s ban on gay marriage and straight civil partnerships, told PinkNews.co.uk that he was pleased at Stonewall’s policy change.

But he added: “It is, however, very disappointing that Stonewall is still refusing to oppose the ban on heterosexual civil partnerships. This stance is de facto support for discrimination. It looks uncaring and sectarian. It doesn’t help build the LGBT-straight alliance that we need to win full equality.”

Mr Tatchell said he would press ahead with the Equal Love legal challenge.

Today’s statement added: “Last February, Stonewall secured a permissive amendment to the Equality Act 2010 to allow the celebration of civil partnerships in religious premises. We look forward to the government implementing this important next step.”

The charity says it will lobby for religions to be given the option of holding marriages if they wish, in the same way that faiths will soon be able to choose whether to hold civil partnerships.

A spokesman said: “It would be a permissive option – as a matter for religious freedom.”

The policy changes comes after Stonewall included a question on the future of civil partnerships in its biennial supporter survey earlier this month. The charity says it does not publicise the detailed findings of its supporter surveys.

Stonewall chief executive Ben Summerskill was accused of not supporting marriage equality at the Liberal Democrat conference last month, where he claimed that allowing straight couples access to civil partnerships could cost £5 billion over ten years.

A week later, at the Labour conference, he said the charity would not be “jumped into” declaring a position on the issue. In 2009, Mr Summerskill told PinkNews.co.uk that “lots of” gays and lesbians do not want the right to marry.

Liberal Democrat MP Stephen Gilbert argued at a fringe meeting that the issue should not be subject to a cost/benefit analysis and said: “It should not be for me as an MP to lobby Stonewall to support gay equality, it should be for Stonewall to lobby me.”

A Populus opinion poll for the Times in June 2009 found that 61 per cent of the public believe that ‘gay couples should have an equal right to get married, not just to have civil partnerships’. Only 33 per cent disagreed.