No church will ever be forced to conduct a gay wedding under new legislation for equal marriage, Culture Secretary Maria Miller has promised.

Setting out the Government's plans to allow same-sex marriage, Mrs Miller said she was putting in place a "quadruple legal lock" guaranteeing watertight protection for religious organisations.

She told the House of Commons in a statement that she was building on Article 9 of the European Convention on Human Rights, which protects the right to freedom of religion. Mrs Miller said she would now continue to consult on how best to implement the Government's plans in legislation to be introduced early in the new year.

"I am absolutely clear that no religious organisation will ever be forced to conduct marriages for same-sex couples, and I would not bring in a Bill which would allow that," she said. "European law already puts religious freedoms beyond doubt, and we will go even further by bringing in an additional 'quadruple legal lock'. But it is also a key aspect of religious freedom that those bodies who want to opt in should be able to do so."

Chief executive of gay rights campaigners Stonewall, Ben Summerskill, said: "We're particularly pleased that ministers have been persuaded to extend their original proposal in order to permit same-sex marriages for those religious denominations that wish to hold them. This is an important matter of religious freedom."

However, opponents accused ministers of ignoring a petition signed by 500,000 people in their formal response to the consultation on same-sex marriage. Colin Hart, campaign director of the Coalition For Marriage, said: "The decision to ignore a petition of half a million people is disgraceful and undemocratic and goes against assurances from civil servants that all submissions would be treated equally and fairly. There were serious flaws with the consultation; not only was it loaded in favour of ripping up the centuries-old definition of marriage, but lacked even the most basic of safeguards to check the identity of those taking part."

In the Commons, a series of Conservative backbenchers rose to condemn the plans. Martin Vickers said it was a "major social change that many of those we represent find unacceptable". Richard Drax demanded: "I would like to ask the Secretary of State and the Government what right have they got, other than arrogance and intolerance, to stamp their legislative boot on religious faith?"

For Labour, shadow home secretary Yvette Cooper condemned the "hysterical" language used by opponents of change and said that continuing to deny gay people the right to marry would be "unfair and out of date". "Those who argue marriage should never change are out of touch with public feeling," she said. The move was welcomed by the Quakers, who have said they intend to conduct same-sex ceremonies in their meeting houses. Paul Parker, the Recording Clerk for Quakers in Britain, said: "The day the first same-sex couple can marry in their Quaker meeting will be a wonderful day for marriage, and a great day for religious freedom in Britain."

However, veteran human rights campaigner Peter Tatchell denounced the exemption for the Church of England and the Church in Wales as "a disappointing fudge" which could be open to legal challenge. "Exempting the official established church sends the wrong signal. There is no reason why these churches should be treated differently from other faiths," he said. "The Government is treating two churches differently from all other religions. Discriminating between faith groups is probably illegal under the Human Rights Act and the European Convention on Human Rights."

The Catholic Church stepped up its opposition to same-sex marriage, accusing ministers of ignoring a 600,000-signature petition supporting the status quo. Archbishop Vincent Nichols, the leader of the Roman Catholic Church in England and Wales, and Archbishop Peter Smith, the Archbishop of Southwark, said opponents of gay marriage should lobby MPs "clearly, calmly and forcefully, and without impugning the motives of others".