More than a third of the venues currently used for marriage parties will refuse to let gay and lesbian couples celebrate civil partnerships when these become law later this year, according to the country's leading firm of gay wedding planners.
The scale of the opposition has infuriated equality campaigners, who have welcomed civil partnerships - the first official recognition for same-sex couples. It has also been condemned by the equality minister, Meg Munn.
The Stonewall campaign group has appointed Bindmans, a leading law firm, to bring legal challenges against venues that refuse to host same-sex ceremonies. They may also face boycotts.
Under the new legislation, gay and lesbian couples will be able to make a legal commitment giving them the same rights and responsibilities as heterosexual married couples, including pension rights and next-of-kin status.
There is concern that some register offices have joined the opposition. All offices will be required to provide civil partnership registration. But it is up to individual local authorities whether same-sex couples can have a ceremony at the register office as well.
So far, two councils, Bromley in Kent and Lisburn in Northern Ireland, have banned gay ceremonies, while a significant minority has yet to make a ruling.
Britain's 174 register offices are meeting this week to address the issue. Richard Edwards, spokesman for the Association of Register and Celebratory Services, said the majority of offices have not been able to give gay couples clear information on whether ceremonies would be allowed.
The decision on allowing ceremonies is made by councillors, not the register office itself. The leader of Conservative-run Bromley council in south London, Stephen Carr, said: "It cannot be a marriage because a marriage is between a man and a woman. I believe that undermining family values is dangerous."
Ms Munn, minister for women and equality, called the opposition "extremely unfortunate". Ben Summerskill, chief executive of Stonewall, said: "We are desperately disappointed that civil partnerships may be overshadowed by this prejudice. The Government could easily have solved the problem by amending the new protections for religious communities in the Equality Bill with similar protection for gay people."
He added that thousands of people, straight and gay, were likely to boycott hotels and venues that refused to host civil partnership ceremonies. "These sorts of incidents show that homophobia is still alive and well," he said.
Gino Meriano, founder of Pink Weddings, the UK's biggest gay wedding company, said 35 per cent of wedding venues are not prepared to host ceremonies for same-sex couples. "Sometimes they say outright, 'no, we're not interested', sometimes it's because they don't know enough about it."
Current laws do not protect gay and lesbian people from being discriminated against in the goods, facilities and services sectors. But Ms Munn told The Independent on Sunday that the Government hoped to introduce measures to outlaw such discrimination within three years.