Daniel Ginnes carried a banner declaring: "No More Mr Nice Gay." Brian Lindsey held up a sign billing Joseph Smith, founder of the Church of the Latter Day Saints, as a "prophet, polygamist, paedophile." Hundreds of others simply chanted: "Mormon scum."

More than 2,000 gay rights protesters marched on a Mormon temple in Los Angeles on Thursday, throwing the church and its followers on to the front line of the battle over California's decision to ban same-sex marriage.

Earlier this week, 52.5 per cent of voters in the supposedly liberal state decided to back Proposition 8, a ballot measure that adds 15 words to the constitution, saying that: "Only a marriage between a man and a woman is valid or recognised in California."

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The development marked a massive setback for gay rights and left 18,000 couples, who had married in the five months since California legalised same-sex weddings, in legal limbo.

In the large and traditionally laid-back gay community, it also left a sense of injustice. Proposition 8 passed with the assistance of a $70m (£44m) campaign largely funded by out-of-state donations from Mormons. "It's taken something like this to make us realise the need to be more aggressive and angry and active," said Mr Ginnes, a graphic designer from West Hollywood. "People didn't think they were going to lose the vote, so they didn't realise it was worth fighting for.

"Now we have lost a fundamental right. That's a shame, but it's certainly galvanised a community that was apathetic. What you are seeing today is the birth of a movement."

In the coming days, a string of protests are planned across California, as campaigners mount a robust PR war against the Utah-based church. Many will picket services tomorrow.

"We should have got nasty a long time ago," said Mr Lindsey, who is originally from a Mormon family. "I'm not going to be polite any more, I'm not going to step around my belief that this is a nasty church with disgusting views which managed to buy an election. I don't care if it's people's religion. I'm going to stand up and fight it."

Thursday's protest, which gridlocked traffic in Hollywood for the second consecutive day, was mostly disciplined, with police reporting two arrests. Seven people were detained at a demonstration on Wednesday.

For the Mormon Church, it threatens a PR nightmare. The gay rights lobby boasts scores of prominent celebrity supporters who have already pledged vociferous support to the campaign to overturn Proposition 8.

The country music singer Melissa Etheridge, a prominent lesbian, announced yesterday that she will refuse to pay income tax until she's "allowed the same rights" as other taxpayers. Instead, she pledged to donate money to legal challenges arguing that the way Proposition 8 was put to the voters was unconstitutional.

Behind the scenes, the mood is turning increasingly ugly. "If they're going to vote away my rights based on fear and ignorance and prejudice, I'm going to give them something to be fucking scared of," read a message posted on the online bulletin board Queerty.

The Mormon Church is in damage limitation mode. "No one on either side of the question should be vilified, harassed or subject to erroneous information," it said in a statement.

The Mormons A snapshot



*The Church of Jesus Christ of Latter Day Saints was founded by Joseph Smith Jr in New York state in 1830 and developed by Brigham Young who migrated with the new Mormons to Salt Lake Valley, Utah, in 1847.



*There are 12 million membersworldwide who believe their church is a restoration of the Church asconceived by Jesus and that other Christian churches have gone astray.



*It is said to be the fourth largest Christian denomination in the whole of the United States.



*Mormons oppose homosexuality, abortion, sex outside of marriage, alcohol, drugs, pornography, gambling, tobacco, tea and coffee.



*Mormons hold that we all have an eternal life stretching either side of our life on earth. They believe that humans can become like gods in the afterlife, although subordinate to God.



*The Church of the Latter Day Saints tolerated "plural marriage" before the American Civil War. The practice was discontinued more than a century ago, but several thousand renegade Mormons in the western states still practise polygamy and the issue is one of the main obstacles to the religion being accepted as a mainstream branch of Christianity.