THE former Archbishop of Canterbury Lord Williams has said that, while modern marriage has lost most of its connection to Christianity, there is still plenty to celebrate in society's attitude to relationships.

Speaking at a discussion on marriage hosted by the law firm Winckworth Sherwood last week, Lord Williams said that Christians should not use the law to make marriage more Christian or promote the institution, but only to protect those within marriages.

"There is no point in expecting the law to fight theological battles on our behalf," he said. "[But] the cultural strength of the desire for public acts of commitment hasn't changed. Whatever you think about gay marriage, it is significant that public commitment is what people most want to affirm in existing relationships." Recounting a conversation with a gay friend, Lord Williams said that it seemed that what gay people wanted from marriage which they did not have with civil partnerships was this public act of commitment.

Despite much negative comment from Christians on declining numbers of marriages and rising divorce rates, Lord Williams said that the situation was not as bleak as some imagined. "It's still just about true that the majority of children are born within marriage," he said. "People want their relationships to be more than just casual and private."

The discussion, "Marriage: Love or Law?", also heard that just 58 per cent of marriages today ended with the death of one spouse rather than divorce.

Lord Williams criticised what he called the "marketisation" of modern marriage, which, he argued, was "an aspect of the short-term and emotionally unintelligent time we live in". He also attacked the unrealistic romanticising of the idea of marriage: "The perfect relationships crystallised in the perfect wedding day - the massive fantastical experience which you go through on your wedding day and which is never quite so good again. We need to look critically at the romantic influence on marriage, especially the marketisation of the experience of marriage."

The debate also featured contributions from the psychotherapist Philippa Perry, the writer and campaigner Melissa Benn, and Professor Rebecca Probert from Warwick University. Professor Probert told the event, at Winckworth Sherwood's offices in London, that the most significant shift in marriage in the past 60 years had been the huge increase in cohabitation.

"In 2011, 78 per cent of couples marrying religiously gave the same address when getting married," which implied they had lived together before getting married, she said. She also discussed the "common-law marriage" myth, in which people who were co-habiting believed they had comparable legal rights and protections to those who were actually married.

A survey released last week by Co-operative Legal Services found that one third of people wrongly believed that those who lived together had the same financial rights as married couples. The poll also suggested that just one in four unmarried couples living together saw cohabitation as a step towards marriage in the future. One fifth said that they had moved in together to reduce living costs. The total number of cohabiting couples has more than doubled since 1996 to almost six million.

Lord Williams, who has been married for 32 years, also criticised the rise in the use of pre-nuptial agreements. "If relationships need to be governed by contract, we may find we have problems in the relational and ethical register arising from that," he said. After the discussion, a number of questions from the audience, which included several family lawyers, centred on divorce settlements and pre-nuptial agreements.

But the real challenges to lifelong marriages came elsewhere, Lord Williams suggested. He referred to changing working patterns, longer life expectancy, and the "marginalisation of young men" in modern culture as possible factors.