London, England - The Archbishop of Canterbury, Dr Rowan Williams, has attacked the Government for undermining marriage and warned that new plans to give similar rights to cohabiting couples could hasten its decline.
Dr Williams told a Sunday newspaper that marriage had "suffered a long process of erosion" and Law Commission proposals would further add to a "prevailing social muddle".
The long-term result could be increased family breakdown, with dire consequences for children, he suggested.
The commission, the Government's law reform advisers, said last month that unmarried couples should be treated like their married counterparts in the event of a split.
Under its proposals, couples who had a long-term relationship could be ordered to sell their home, pay lump sums to each other and share pensions if they go their separate ways.
The commission, headed by Sir Roger Toulson, a High Court judge, insisted that the measures would not damage the institution of marriage by encouraging couples to live together rather than take vows.
It suggested that the proposals could actually encourage more people to marry because partners would no longer be able to escape financial responsibilities by living together but not making a commitment.
But Dr Williams said the proposals would further dilute the unique status of marriage, which Christians view as a cornerstone of society.
"The concept of cohabitation is an utterly vague one that covers a huge variety of arrangements," Dr Williams told The Sunday Times. "As soon as you define anything, you create a kind of status that is potentially a competition with marriage or a reinvention of marriage. One of the problems is trying to solve individual and infinitely varied problems by legislation."
He said that the proposals showed "very proper concern for vulnerable people left stranded at the end of a partnership breaking up". But those "anxious" about the needs of a cohabiting partner could already make wills and draw up legal contracts.
The evidence showed marriage to be the most stable form of union and was therefore more likely to create a healthy environment in which to raise children.
"I don't think I need to spell out the research about educational factors that can be traced in children from unstable or broken partnerships.
"That's not to say that single parents don't do heroic things and it's not to say that cohabiting couples aren't often excellent parents day-by-day.
"The question is about what institution in the long run best serves those needs."
He said the abolition of the tax advantages of marriage had sent out an unhelpful signal.
Dr Williams reflected the anger of many bishops over the way the Government introduced civil partnerships, which are widely seen as the same as civil marriage for gays.
"Civil partnerships were specifically distinguished from marriage as a set of civil contracts that didn't necessarily involve sexual partnerships," he said. "Some government documents suggest a kind of slippage of the understanding about that."