LONDON - Championing a cause eschewed by fellow conservatives elsewhere, the British government said Tuesday that it would sponsor a bill to allow same-sex couples to marry, including in churches, synagogues, and mosques that look favorably on such unions.

Religious organizations against the idea would be legally protected from having to wed gays and lesbians, and the Church of England, as the nation's established church, would specifically be barred. But civil marriage would be available to all couples under the new proposal.

The bill is likely to be introduced next month and voted on sometime in the new year. Although church groups and some lawmakers have spoken out vehemently against opening up marriage to same-sex couples, polls show that a majority of Britons support the idea, and the legislation is almost certain to pass.

If so, Britain would become the latest European country to give gay and lesbian residents the right to get hitched.

The proposal is unusual because the sponsoring government lies on the right of the political spectrum. Supporters of marriage equality were delighted last year when Prime Minister David Cameron declared at a party conference: "I don't support gay marriage despite being a Conservative. I support gay marriage because I'm a Conservative."

That stance is far from universal within his party.

"These proposals are a constitutional outrage and disgrace," thundered one Tory member of Parliament, Stewart Jackson. "There is no electoral mandate for these policies."

As many as 100 Tory lawmakers in the 650-seat House of Commons, including members of Cameron's cabinet, could vote against the measure.

Suporters say the bill will contain a "quadruple lock" of safeguards to guarantee that no religious groups will be compelled to perform same-sex weddings against their will.

For example, only a religious institution's overall governing body would be able to decide whether the organization will "opt in" on marrying gay couples. If it decides not to, individual ministers within that group could not take it upon themselves to perform such ceremonies.

The bill will explicitly forbid same-sex marriages in the Church of England because of its special status as the established church.

Currently, gay and lesbian couples can enter into civil partnerships in Britain that carry virtually all the rights of marriage. About 50,000 partnerships have been registered since 2005.