Cardinal Keith O'Brien, the leader of the Catholic Church in Scotland, who is also the most senior Roman Catholic cleric in Britain, has warned against plans to legalize gay marriage, saying it would "shame the United Kingdom in the eyes of the world."
The efforts to change the traditional definition of marriage from a union between one man and one woman to include homosexual couples have been championed by British Prime Minister David Cameron, but he faces opposition both from the Church of England and the Catholic Church in Scotland, two of the largest religious institutions in the United Kingdom.
Last week, the Archbishop of Canterbury, Dr. Rowan Williams, who has spoken out against violence directed against homosexuals, insisted that the government has no right to try to change the definition of marriage by making it more inclusive, The Telegraph reported.
Similarly, Cardinal O'Brien has hit out against Prime Minister Cameron, describing plans to legalize same-sex marriage as a "grotesque subversion of a universally accepted human right," The Sunday Telegraph reported.
"Since all the legal rights of marriage are already available to homosexual couples, it is clear that this proposal is not about rights, but rather is an attempt to redefine marriage for the whole of society at the behest of a small minority of activists," the Cardinal wrote in an opinion piece.
"Redefining marriage will have huge implications for what is taught in our schools, and for wider society. It will redefine society since the institution of marriage is one of the fundamental building blocks of society. The repercussions of enacting same-sex marriage into law will be immense," he warned.
Cardinal O'Brien even compared legalizing gay marriage to legalizing slavery, explaining that churches would be forced to marry homosexual couples even if the government tried to assure them of the contrary.
British government officials, such as Scottish Secretary Michael Moore, have attempted to assure religious groups that they will not be forced to endorse same-sex marriages.
"We're not seeking to change religious marriage and we're not seeking to impose it on religious groups," Moore told BBC. "What we are saying is that where a couple love each other and they wish to commit to each other for their life then they should be able to have a civil marriage irrespective of their sexual orientation."
Labour deputy leader Harriet Harman has also lent her support for same-sex marriages.
"I don't want anybody to feel that this is a license for whipping up prejudice. What you're talking about is individual people and their personal relationships, their love for each other and their wanting to be in a partnership or getting married. I think we should support that," Harman argued.
Civil unions have been in effect in Britain since 2005, which gave same-sex couples the same legal rights as married couples. Up until now, however, the law did not allow such unions to be referred to as marriages.
Another step toward gay marriage has been identified as the 2011 law which allowed civil partnership ceremonies to be conducted in places of worship in England and Wales.