LONDON — A gay marriage bill that has divided Britain’s ruling Conservatives but is backed by their leader, Prime Minister David Cameron, was debated in Parliament ahead of a key vote Tuesday.

If entered into law, the bill would enable same-sex couples to get married in both civil and religious ceremonies, provided that the religious institution consents.

“The depth of feeling, love and commitment is no different between same-sex couples than opposite-sex couples,” Culture Secretary Maria Miller said. “This bill enables society to recognize that commitment in the same way, too, through marriage.”

The proposals are championed by Cameron and senior officials, but dozens of Conservative lawmakers are expected to vote against the bill. Around 20 party members wrote to Cameron on Sunday, urging him to delay the vote and arguing that the party would lose significant numbers of votes in the next election as a result of backing it.

Nonetheless, it is expected to pass with support from the vast majority of lawmakers from the left-leaning Labour Party and Liberal Democrats.

Officials have stressed that all religious organizations can decide for themselves if they want to “opt in” to holding gay weddings. However, the Church of England, the country’s official faith, is barred from performing such ceremonies unless it changes its laws.

The bill would also allow couples who had previously entered into civil partnerships to convert their relationship into a marriage.

In a letter published in the Daily Telegraph newspaper Tuesday, senior Conservatives including Foreign Secretary William Hague and Home Secretary Theresa May urged fellow party members to support the proposals.

“Marriage has evolved over time. We believe that opening it up to same-sex couples will strengthen, not weaken, the institution,” they wrote. “This is the right thing to do at the right time.”

If passed, the bill’s provisions would come into effect in 2015, ahead of the next election.

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