Image caption The government says the fears of the Church are unfounded

Downing Street has defended plans to change the status of civil ceremonies to allow gay and lesbian couples in England and Wales to get married.

It said it was confident safeguards to stop religious organisations being forced to take part in services would not be overturned by European courts.

The Church of England has said the move would "alter the intrinsic nature of marriage as the union of a man and a woman".

Ministers plan to pass the law by 2015.

In its 11 June response to a consultation on the issue, the Church of England said plans to exempt religious organisations from performing gay marriages would be unlikely to survive legal challenges in domestic and European courts.

However, Home Secretary Theresa May has said she believes ministers can create safeguards to protect the concerns expressed by religious groups.

Analysis If the state sanctions marriage between same-sex couples, and one of those couples is deeply religious and wants their marriage ceremony to take place in a church or other place of worship, could they bring a legal challenge? The answer is yes, and the basis is article 9 of the Human Rights Act which protects freedom of thought, conscience and religion. Any such challenge would be likely to end up at the European Court of Human Rights and would be against the UK government's decision to legalise only gay civil marriages, and ban religious ones. Like the blanket ban on prisoner voting, it is entirely possible that the European Court would declare the restriction unlawful. However, critically, that would not compel religious institutions to carry out same-sex marriages. It would be more likely to allow religious institutions to choose whether to marry gay couples, and indeed allow individuals within those institutions to choose whether to conduct religious ceremonies. That would lead to a patchwork landscape for those seeking a same-sex religious marriage, with couples having to shop around. It could also lead to ructions within a religion where the governing body remains against same-sex marriage, but individual members of the clergy decide that they are content to perform a religious ceremony.

"The government is not going to ask anybody to do anything that is against their conscience," she said.

"We want to ensure that we can put into place a framework that makes sure that those people who don't want to host same-sex marriages are not required to do so."

Civil partnerships were introduced in 2005 to give same-sex couples the same legal rights as married couples, but the law does not allow such unions to be referred to as marriages.

The government rejected the Church of England's assertion that the consultation exercise, which closes on Thursday, was "flawed, conceptually and legally".

Downing Street said the government welcomed the submission by the Church of England and would carefully consider it.

But the prime minister's spokeswoman confirmed that the government still intended to legislate on gay marriage by the end of this parliament.

"It is the government's view that marriage is one of the most important institutions we have got," she said.

"The consultation paper makes very clear that no religious organisation will be forced to conduct same-sex marriages as a result of our proposals."

She added that the government had taken legal advice on the likelihood of a challenge to the European court before drawing up its proposals and that Tory MPs, some of whom had expressed opposition to the plans, would be given a free vote.

Meanwhile, the National Secular Society said it was "incorrect" for the Church of England to "usurp Parliament's power" by claiming it could not redefine marriage.

Home Office consultation paper proposals to allow same-sex couples to marry in a register office or other civil ceremony

to retain civil partnerships for same-sex couples and allow couples already in a civil partnership to convert it into a marriage

to allow people to stay married and legally change their gender

to maintain the legal ban on same-sex couples marrying in a religious service Source: Home Office consultation paper

"The Church's case rests on the risible proposition that introducing same-sex civil marriage will render the Church vulnerable to a European Court forcing it to conduct same-sex religious marriages too. The freedom of religion provisions, however, would ensure this could never happen," it said.

Gay rights campaign group Stonewall described the latest concerns raised by the Church of England as "scaremongering"

The Catholic Church in England and Wales has urged people to sign an online petition organised by the Coalition for Marriage.

More than 550,000 people have so far signed the petition set up by the "umbrella group of individuals and organisations in the UK that support traditional marriage and oppose any plans to redefine it".