Churches in the UK could be forced to celebrate same-sex marriages, despite repeated promises by Prime Minister David Cameron (pictured) to exempt them.

Both the Church of England and Roman Catholic Church have already voiced fears that the Government’s pledge would not withstand a challenge in Parliament or the courts.

In its official response to the Government’s proposals on same-sex marriage, the Church of England warned that churches may eventually be forced to conduct such ceremonies.

In the document, “A Response to the Government Equalities Office Consultation -“Equal Civil Marriage”- from the Church of England”, it said: “It is unlikely to prove politically sustainable to prevent same sex weddings in places of worship given that civil partnerships can already be registered there where the relevant religious authority consents.  

“And there have to be serious doubts whether the proffered legal protection for churches and faiths from discrimination claims would prove durable.”

Meanwhile, Crispin Blunt, the prisons minister, said that Government plans for a blanket ban on religious groups from carrying out gay marriages could prove “problematic legally”. He added the promised exemption for religious groups may not survive even the initial Parliamentary process, the Daily Telegraph reports.

In addition, Desmond Swayne, a senior aide to David Cameron said that churches which want to marry gay couples should be free to do so. The Home Office also confirmed that it was “listening to” some religious groups who have said that they would like to carry out same-sex weddings.

The Catholic Church also published its formal response [LINK] to the Government consultation on same-sex marriage accusing the Government of ignoring democratic opposition to the proposals.

In a 10-page submission, the Archbishop of Southwark, the Most Revd Peter Smith, says the Coalition has “no electoral mandate” to impose such as a “radical change” in social policy which would have unpredictable and irreversible consequences.

In his submission Archbishop Smith echoes concerns from the Church of England that any exemption for religious groups is likely to be overturned.

He added: “It is of serious concern to the Bishops therefore that this proposal, which has the potential to impact so immensely on the social stability of our society and which has significant implications for the unique institution of marriage and of family life, appears not to have been subject to such careful study and analysis.”

In the consultation document Theresa May, the Home Secretary, makes clear that same-sex marriage would only apply to civil weddings excluding churches, mosques and synagogues.

“The Government is not seeking to change how religious organisations define religious marriage and any subsequent legislation would be clear that no religious organisation could conduct a religious marriage ceremony on religious premises for same-sex couples,” the document says.

Meanwhile, the UK’s advertising watchdog has ruled that opposing gay marriage is not offensive or homophobic.

The Advertising Standards Authority (ASA) threw out a series of complaints about publicity material for the Coalition For Marriage campaign which claimed that they would offend homosexuals.

The watchdog ruled that, while not everyone would agree with the aims of the campaign, this was no grounds for claiming that they were discriminatory.

A total of 11 people complained that advertisements which appeared in Country Life Magazine and Archbishop Cranmer, a popular political and religious blog, were homophobic.

The advertisement showed a montage of wedding photographs under the words “I Do” and details of a poll suggesting that 70 per cent of people wanted to “keep marriage as it is”.

It added: “Whilst fully recognising the rights and views of others, we’re asking you to support us.

“If you want to keep the true meaning of marriage as it is, and has been for thousands of years, say ‘I do’ – by signing our petition at c4m.org.uk.”

In its adjudication the ASA ruled: “We noted the complainants believed that [the] ads … were offensive as they considered them to be homophobic.

“However, the ads focused on the current legal definition of marriage and its history.

“We considered that, although some people might disagree with the advertisers’ opinions on the matter of same sex marriage, the ads in themselves did not contain anything that was likely to cause serious or widespread offence.”

Meanwhile, in Denmark, all churches will be required to offer same-sex marriages after a new law was passed in the Danish parliament by a large majority.

Under the new law, an individual priest can refuse to perform a same-sex ceremony, but the local bishop must supply a replacement.